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The 8 Best Long Underwear for Men

We put 18 pairs of the best long underwear for men to the test and find the best and warmest options on the market, and these are our picks.
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Best Long Underwear Men Review
Credit: Justin Simoni
By Justin Simoni and Aaron Rice  ⋅  Mar 21, 2025

The Best Long Underwear for Men


Cold winter days have you layering up? A pair of great long underwear bottoms are core to every effective layering system, helping to retain body heat in the face of dipping temps and easily releasing moisture once you get moving.

We've been testing long underwear for men for over a decade, so we can now showcase the very best options in this review. Our team of experts spent months layering up through every season with high and low-intensity outdoor activities to test these layers, taking them on river trips, ski slopes, and cold winter trail runs. We backed up our field research with objective, lab-style tests designed to analyze specific features of each pair of long johns.

It's hard to go wrong with Smartwool Classic Thermal Merino Bottoms. They add a serious warmth factor and are some of the most comfortable bottoms we have worn. If you are willing to invest, the Artilect Boulder 125 is a great ultralight choice that offers great breathability and drying speed.

If you want a complete set, our write-up on the best base layer tops can help you determine what to pair with our favorite bottoms reviewed here. Next, pick out some cozy socks, and you'll be well on your way to adventure-ready. If you need some new outer layers, a lightweight down jacket can be a good place to start.

Editor's Note: We updated this review on March 21, 2025, adding more products from Amazon Essentials, Merino.tech, and Arc'teryx.

Related: Best Long Underwear for Women

Top 18 Long Underwear

Displaying 1 - 18 (scroll right)
 
Awards Editors' Choice Award
Best Synthetic Long Underwear for Men
Editors' Choice Award
Best Overall Long Underwear for Men
Top Pick Award
Best Lightweight Long Underwear
Best Buy Award
Best Synthetic Bang for the Buck
Top Pick Award
Best Midweight Long Underwear for Men
Top Pick Award
Our Favorite 3/4 Length
    Top Pick Award
Excellent Value for Cold Winter Days
  Best Buy Award
Our Favorite Merino Wool on a Budget
    
Price $84.00 at Amazon
Compare at 2 sellers
$109.99 at Amazon
Compare at 4 sellers
$120 List$55 List
$54.95 at REI
$80 List
$79.99 at Amazon
$120.00 at Backcountry
Compare at 3 sellers
$89.00 at REI$99 List
$48.92 at Backcountry
$75.00 at Amazon$83.96 at Evo$60 List
$59.99 at Amazon
$80 List
$79.95 at REI
$64.99 at Evo$59 List
$58.99 at Amazon
$85.99 at Amazon$30 List
$30.99 at Amazon
$40 List
$29.99 at Amazon
$21 List
$20.90 at Amazon
Overall Score Sort Icon
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Pros Fuzzy inner face perfect to capture heat, smooth outer face enhances layerability,
can be casually worn as an outer layer
A nice balance of warmth and breathability, super cozy, nicely articulated designExtremely breathable, ultralight stretchy nylon/Merino wool blendTough synthetic fabric, four-way stretch for great range of motion, excellent performance for the priceSoft and stretchy wool fabric, super cozy and warm, high waist and tall ankle cuffsShorter length reduces bunching near ankles, seamless panels provide additional articulation and ventilation only where needed, high waist and thick waistband keep bottoms in place100% recycled polyester, light fabric weight, impressive loft and warmthBreathable, highly efficient wicking, comfortable Merino/recycled polyester blend, impressively durableFun colors and patterns, soft and comfy 100% Merino wool, thick and supportive waistband, 3/4 length is warm for the weightAthletic fit hugs body for great breathability, extra wide waistband keeps layer in place, stretchy wool blend materialAffordable intro to Merino, warm and cozy, wide spectrum of available sizesExcellent warmth for the weight, perfect for summer nights, simple design stays out of the way, gusseted crotchGood warmth to weight ratio, breathable 100% wool fabric, durable, comfortable gusseted crotch designFlatlock seams throughout, soft and comfy 100% Merino wool, excellent price point for materials and qualityWarm, lightweight, breathable, versatile, comfortable, great thermoregulationAffordable, nice thick waistband, extremely stretchy synthetic materialInexpensive, lightweight, quick-dryingInexpensive
Cons Weighs more than other options, thick fabric has poorer breathability, priceyExpensive, stretches out in between washes, slow to dry when saturatedPrice may make you do a double-take, care instructions need to be followed when dryingHeavier than wool bottoms for their warmthLacking in durability, takes a long time to line dry, not as breathable as other optionsNo-fly design could be inconvenient underneath other layers, fit may be too tight for some body types, priceyQuestionable durability, saggy bottomNot designed for mid-winter temps, relatively heavy for fabric weight, thin waist bandWool quickly becomes fuzzy, durability an issue for 100% Merino wool fabricNot as warm as the material weight suggests, tight athletic fit may not appeal to everyoneStarts off slightly itchy, simplified construction may not be as comfy, Merino wool is delicateFabric is thin and not very durable, minimal cuffs are especially vulnerable to wear, fit tighter than mostWaistband not as tall as others, 100% wool is not as durable as blended fabrics, fabric will lose some of its stretch over time, potential to shrink100% Merino fabric more delicate than synthetic blends, careful drying required for best lifetime useNot very durableSmall for the labeled size, fabric easily tears from minor abuse, obtrusive stitchingUncomfortably tight fit, pilling after a few washes, not very warm for the weightpoor elastane quality, cotton fabric dries slow, fabric retains little heat,
awkward fit
Bottom Line A furnace-like pair of synthetic bottoms, perfect for either the coldest days outside or the laziest days inDesigned to keep you warm in the coldest conditions, this is a versatile pair of Merino wool bottomsA seriously tuned ultralight pair of wool/nylon blend leggings built for fast and light outdoor adventuresA great synthetic thermal long underwear at an unbeatable price for the warmth and durability they provideFor wintry missions in the backcountry or hibernating deep inside a cabin, these soft, long bottoms are almost perfect for keeping legs extra toastyCarefully engineered 3/4 length thermals with compression pants-like tightness that’ll keep you warm and super comfortable while pursuing high-output activitiesWarmer than most and lighter than the rest, this pair of long underwear redefines what is possible from a synthetic base layerA versatile, lightweight Merino and recycled polyester blend that offers superb breathability and wicking, ideal for any fast-paced adventureBeautiful and bold colors and patterns make these warm and plush 3/4 length long undies hard to forgetAn excellent, breathable, mid-weight wool blended bottom, most attractive to those who can wear its athletic fitGrab a pair of these if you are looking for an affordable and warm pair of Merino wool bottomsFor transitional spring nights, this lighter-weight pair of long bottoms works well to up the heat retention without getting too hotA solid pair of 100% wool leggings at a great weight for a wide spread of temperatures and conditionsThese make for an excellent value pair of 100% Merino wool long underwearA fantastic pair of lightweight Merino bottoms that provide impressive warmth without being too hot, breathe extremely well, and are very comfortableThis inexpensive set of base garments has a smooth exterior and fleecy interior, but we worry that they're not durable enough for serious everyday useA low-cost set of base garments will help keep you warmer, but we don't know if we'd rely on them to get us through the winter unscathedAn extremely conscious cotton/poly thermal layer set
Rating Categories Arc'teryx Rho Heavy... Smartwool Classic T... Artilect Boulder 125 REI Co-op Midweight... Minus33 Kancamagus... Smartwool Intraknit... Patagonia Capilene... Outdoor Research Al... Ortovox 185 Rock'N'... Mons Royale Cascade... Meriwool Merino 250... REI Co-op Merino 18... Icebreaker Merino 2... Merino.tech Bottoms Smartwool Classic A... WEERTI Thermal Flee... Thermajohn Thermal... Amazon Essentials Set
Warmth (25%)
9.0
9.0
5.0
7.0
9.0
7.0
6.0
6.0
7.0
5.0
8.0
7.0
7.0
8.0
5.0
4.0
4.0
5.0
Breathability (20%)
6.0
7.0
10.0
7.0
7.0
7.0
7.5
7.0
8.0
9.0
6.0
6.0
6.0
6.0
8.0
8.0
8.0
7.0
Comfort and Fit (20%)
9.0
8.0
8.0
7.0
7.0
7.0
6.0
7.0
7.0
6.0
7.0
7.0
6.0
6.5
7.0
6.0
5.0
5.0
Durability (15%)
8.0
7.0
6.0
9.0
6.0
8.0
8.0
7.0
4.0
7.0
6.0
6.0
6.0
5.0
5.0
5.0
5.0
5.0
Drying Speed (10%)
9.0
6.0
8.0
7.0
6.0
5.0
8.0
7.0
7.5
8.0
6.0
6.0
8.0
6.0
7.0
9.0
9.0
6.0
Layering Ability (10%)
7.0
7.0
8.0
7.0
7.0
9.0
8.0
8.0
7.0
7.0
6.0
8.0
8.0
7.0
7.0
7.0
7.0
6.0
Specifications Arc'teryx Rho Heavy... Smartwool Classic T... Artilect Boulder 125 REI Co-op Midweight... Minus33 Kancamagus... Smartwool Intraknit... Patagonia Capilene... Outdoor Research Al... Ortovox 185 Rock'N'... Mons Royale Cascade... Meriwool Merino 250... REI Co-op Merino 18... Icebreaker Merino 2... Merino.tech Bottoms Smartwool Classic A... WEERTI Thermal Flee... Thermajohn Thermal... Amazon Essentials Set
Material 53% polyester, 38% nylon, 9% elastane 100% Merino wool Nuyarn: 85% Merino wool, 15% nylon 92% recycled polyester, 8% spandex 100% Merino wool 54% Merino wool, 43% polyester, 2% elastane, 1% polyamide 100% recycled polyester with HeiQ Fresh 47% Merino wool, 47% recycled polyester, 6% spandex 100% Merino wool 81% Merino Wool, 12% nylon, 7% elastane 100% Merino wool 100% Merino wool 100% Merino wool 100% Merino wool 88% Merino wool, 12% nylon core 92% polyester/ 8% spandex 92% polyester 8% spandex 60% cotton, 40% polyester
Insulation Weight Class Midweight/heavyweight Midweight Lightweight Midweight Midweight Lightweight Lightweight Lightweight Midweight Lightweight Midweight Lightweight Midweight Midweight Lightweight Lightweight Lightweight Lightweight
Measured Weight (Size Medium) 9.5 oz 8.3 oz 4.3 oz 7.4 oz 8.9 oz 9.2 oz 5.9 oz 6.8 oz 5.4 oz 5.5 oz 7.9 oz 6.2 oz 6.5 oz 7.8 oz 6.1 oz 6.0 oz (large) 5.8 oz (large) 7.8 oz
Measured Inseam (Size Medium) 32.0 in. 31.0 in 31.0 in 29.5 in 31.5 in 20.0 in 31.3 in 32.8 in 20.0 in 29.5 in 28.5 in 29.5 in 31.5 in 28.8 in 31.8 in 28.0 in (large) 28.0 in (large) 30.8 in
Listed Inseam Length (Size) 32.5 in (medium), short and tall options also available 30.0 in (medium) None listed 28.0 in (medium), 31.0 in tall options 29.0-32.0 in (medium), big and tall options available 21.5 in (medium) None listed 31.0 in (medium) None listed None listed 29.0-32.0 in (medium), tall and large options available 29.0 in (medium) 31.0 in (large) 28.0 in (medium) 30.7 in (medium) 26.0 in (medium) 25.5 in (medium) None listed
Odor Control Fabric None Naturally odor resistant Naturally odor resistant None Naturally odor resistant Naturally odor resistant HeiQ® Pure odor control Naturally odor resistant Naturally odor resistant Naturally odor resistant Naturally odor resistant Naturally odor resistant Naturally odor resistant Naturally odor resistant Naturally odor resistant None None None
Fly? No Yes No Yes Yes No Yes Yes No No Yes Yes Yes Yes Yes Yes Yes Yes
Dryer Safe? No Yes No Yes Yes No Yes No No No No Yes No No Yes Yes Yes Yes
Listed Fabric Weight (g/m²) Not stated 250 g/m² 125 g/m² Not stated 235 g/m2 200 g/m² Not stated 150 g/m² 185 g/m² 180 g/m² 250 g/m² 185 g/m² Not stated 250 g/m² 150 g/m² Not stated Not stated Not stated
3/4 Boot-Cut Available? Yes Yes Yes No No Yes No No Yes Yes No No Yes No Yes No No No

Best Synthetic Long Underwear for Men


Arc'teryx Rho Heavyweight Bottoms


81
OVERALL
SCORE
  • Warmth 9.0
  • Breathability 6.0
  • Comfort and Fit 9.0
  • Durability 8.0
  • Drying Speed 9.0
  • Layering Ability 7.0
Materials: 53% polyester, 38% nylon, 9% elastane | Weight: 9.5 oz (size Medium)
REASONS TO BUY
Extremely warm
Wearable alone in casual settings
Sheer outer face and soft inner face
REASONS TO AVOID
Heavier than other options
Not a bargain option

When you're looking for one of the warmest synthetic long underwear bottoms made, reach for the Arc'teryx Rho Heavyweight. These thick, long johns wear like tight joggers, locking in warmth all through your lower half. If wool fibers don't agree with your skin, these make a great alternative. “These are the long bottoms to grab when you want serious warmth retention in your layering strategy,” notes our main reviewer. A far more sheer outer face complements the fuzzy nap underside of the fabric, trapping heat next to your skin while your top layers easily lay against the Rhos without snagging.

The Arc'teryx Rho Heavyweight Bottoms are excellent mid-heavyweight bottoms, ideal for cold days when warmth is a top priority. But they are not the bottoms for transitional seasons or high-intensity activity. Our tester confirms, “A poor matchup would be to don these on a brisk day for a fast run: you'll quickly overheat, and sweat will start to build up, making them stinky and uncomfortable.” But they will serve well when temperatures drop, and you need to bring the heat. They also come at a high price tag, which means that they won't appeal to everyone. A more adaptable pair of long underwear for cooler conditions is the REI Co-op Midweight Bottoms, which are lighter and far cheaper. Being so thick also means the Rho Heavyweights wear a little heavier than almost every other pair we tested in our lineup. And if you already plan to work up a sweat, such ultra-warm bottoms may not be breathable enough to keep up. The Patagonia Capilene Midweight Bottoms is a much more breathable pair that's excellent for high-output activities.

Read more: Arc'teryx Rho Heavyweight Bottoms review

The Arc'teryx Rho Heavyweight Bottoms are warm enough to wear out as your only layer, with a smart zippered side pocket for small items like keys.
Credit: Justin Simoni

Best Overall Long Underwear for Men


Smartwool Classic Thermal Merino Bottom


76
OVERALL
SCORE
  • Warmth 9.0
  • Breathability 7.0
  • Comfort and Fit 8.0
  • Durability 7.0
  • Drying Speed 6.0
  • Layering Ability 7.0
Materials: 100% Merino wool | Weight: 8.3 oz (size Medium)
REASONS TO BUY
Cozy and comfortable
Terrific thermoregulation
Merino wool-lined waistband
REASONS TO AVOID
Stretches out between washings
Expensive

We adore the Smartwool Classic Thermal Merino Bottom and have given it our top honors. The combined warmth and comfort of these long johns are excellent when the temps really dip down. The special interlock knit provides exceptional breathability, especially considering the thick, 250 g/m² cut of the 100% Merino wool. You'll find rear gussets to match the front, enhancing comfort and fit. Our lead reviewer sang the praises of this design: “The gusseted crotch is a big win for me as I'm riding my bike all year 'round, and getting the seams out of the way is just way more comfortable.” The extra-wide, wool-lined waistband and full-flatlock seams cut down on common complaints of itchiness. While these are designed specifically for cold conditions, their balance of warmth and breathability makes them versatile even when temperatures begin to warm up a bit. “These pants are plush and my ideal companion for full days spent outside through the coldest months of winter,” our lead reviewer adds.

Despite the thick construction — and indeed, these bottoms are one of the most durable all-natural layers we tested — all Merino layers require a certain level of care that goes above and beyond most articles of clothing. With regular use between washings, the SmartWool Classic Thermal Merino tends to stretch out, so you may find it tempting to throw them in the dryer to shrink them back up. But don't! Careful laundering and primarily flat or line air-drying will help improve the longevity of this and all Merino base layers. We know the laundering process can be annoying, but the excellent thermoregulation capability makes this pair well worth the extra effort, especially for those playing or working in frigid climates. If carefully laundering wool sounds like too much of a hassle, a synthetic option like the Arc'teryx Rho Heavyweight Bottoms or REI Co-op Midweight Bottoms may suit you better. They'll last much longer when thrown in the dryer if you desperately need them immediately or if they sneak in by accident. When you put the Classic Thermals away for the season, look into grabbing the Smartwool Classic All-Season Merino Bottom for the rest of the year. What we love about the design of the SmartWool Thermals can also be found in these long bottoms, except the fabric is lighter weight, which is perfect for shoulder season and cold summer nights up high.

Read more: Smartwool Classic Thermal Merino Bottom review

These thick bottoms are easy to put on, and wear somewhat fitted on our tester's large legs.
Credit: Justin Simoni

Best Synthetic Bang for the Buck


REI Co-op Midweight Bottoms


73
OVERALL
SCORE
  • Warmth 7.0
  • Breathability 7.0
  • Comfort and Fit 7.0
  • Durability 9.0
  • Drying Speed 7.0
  • Layering Ability 7.0
Materials: 92% recycled polyester, 8% spandex | Weight: 7.4 oz (size Medium)
REASONS TO BUY
Withstands harsh use
Low-cost, high performance
Cozy four-way stretch fabric
REASONS TO AVOID
Not as warm for the weight as wool

Back from a total redesign, we're now even more impressed by the REI Co-op Midweight Bottoms as a value-driven, super tough, and no-nonsense pair of synthetic long undies. Our last critiques must have been heard at REI World Headquarters, as these long johns feature a much improved-upon four-way stretch poly-spandex fabric that we adore. The bombproof durability and warmth of the Midweight remain, as does the overall understated cut and design — which is snug but not athletically tight — a fit that we think works great for most people partaking in most activities. “The REI Midweights are one of the burliest pairs I've tested, thanks to their heavier synthetic fabric and tight weave,” reports our lead reviewer. It's the warmest synthetic mid-layer we've tested, giving even some 200 g/m² thick 100% Merino wool thermal underwear a run for their money. Notably, during field testing, these delivered even on high peaks in heavy winter conditions — the ultimate test of warmth, when performance really matters.

Since REI updated the Midweight Bottoms, there are even fewer attributes we can point to as weaknesses. This no-nonsense piece of gear gets the job done well enough and isn't looking to collect accolades. Their performance is tough to beat, considering the price. But If you're in the market for an even warmer layer (and maybe a softer and comfier one), it could be time to reach for a wool option like the Smartwool Classic Thermal Merino Bottom and leave midweights like these for a milder day. If you want to stick with synthetics, one of the only warmer pairs you'll find is the Arc'teryx Rho Heavyweight Bottoms, whose fleece-lined inner face is on another level of warmth, likely the warmest synthetic long underwear in our lineup and matching — or even bettering — the toastiest Merino wool bottoms we've tested.

Read more: REI Co-op Midweight Bottoms review

The synthetic fabric of the REI Co-op Midweight Bottoms dry faster than most of the comparable wool bottoms on our line dry tests.
Credit: Justin Simoni

Our Favorite Merino Wool on a Budget


Merino.tech Bottoms


66
OVERALL
SCORE
  • Warmth 8.0
  • Breathability 6.0
  • Comfort and Fit 6.5
  • Durability 5.0
  • Drying Speed 6.0
  • Layering Ability 7.0
Materials: 100% Merino wool | Weight: 7.8 oz (size Medium)
REASONS TO BUY
good stitching and low-profile seams
plush fine spun 100% Merino wool
great value for Merino
REASONS TO AVOID
Fabric lacks great durability
Line dry needed for best lifespan

We're always on the lookout for quality products found at a good value. The Merino Tech Bottoms impressed us by delivering a pair of soft, comfortable, and super warm thermal underwear at a price we can justify — even when on a budget. “If you're looking to grab your first pair of wooly bottoms, I would not hesitate to recommend these as a solid choice,” notes our lead reviewer. The key is the fabric's super finely spun 100% Merino wool and thoughtful construction using low profile, strong flatlock seams. The next-to-skin fit will move with you while you're skinning up a mountain and wick moisture away from the body as you sweat.

For all its admirable qualities, the material choice is also one of the biggest weaknesses of the Merino Tech Bottoms. Wool is a more delicate fabric, so to preserve the lifespan of your leggings, it will be important to layer them under a more protective outer pant to avoid tearing against abrasive surfaces. You should also treat such fabric with tender, loving care when washing and drying. Although Merino.tech states these are dryer-safe, our test team has reservations and would still suggest drying these on the line or laying them flat to dry. Other entry-level options exist in our lineup, especially if your budget is really tight. Synthetic or cotton-synthetic blends like the Amazon Essentials Set and WEERTI Thermal Fleece Lined Set fall into this category. Still, neither will be as warm, breathable, or activity-ready as the Merino.tech. The Merino Tech Bottom makes a good pair of long bottoms for cold, active days: ski touring, snowshoeing, or a very cold run. If you need warmth, another excellent Merino wool choice similar to the Merino Tech Bottoms is the Meriwool Merino 250 Bottom, which can be found at a similar price and offers comparable performance.

Read more: Merino Tech Bottoms review

Hard to believe for the price, but the Merino.tech Bottoms are made of bonafide 100% merino wool.
Credit: Justin Simoni

Best Lightweight Long Underwear


Artilect Boulder 125


74
OVERALL
SCORE
  • Warmth 5.0
  • Breathability 10.0
  • Comfort and Fit 8.0
  • Durability 6.0
  • Drying Speed 8.0
  • Layering Ability 8.0
Materials: Nuyarn (85% Merino wool, 15% nylon) | Weight: 4.3 oz (size Medium)
REASONS TO BUY
Extremely breathable
Ultralight
Stretchy, nylon-Merino wool blend
REASONS TO AVOID
Quality like this is not cheap
Imperative to follow the wash/dry instructions closely

Meticulously crafted, the Artilect Boulder 125 leggings use advanced composite materials like comfy, warm 125 g/m² Nuyarn (an 85% Merino, 15% nylon blend). These bottoms also have a complex panel pattern with literal speed holes/perforations built-in. The eyelets act almost like the pores on your skin, allowing perspiration to easily exit from the skin and fabric into the air. All this will keep you perfectly thermoregulated on your next light and fast mission through chilly conditions. And even though you'll most likely wear these under a pair of pants or tights, they look pretty darn good all on their own when you're lounging around your house or in the back of your van.

In step with their speed-over-everything philosophy, the Boulder 125 isn't meant to be an all-rounder. Wear them when the weather is fairly mild, and swap them out for something more substantial on those colder winter missions. “The Artilects just don't have enough weight to be useful in the colder, darker months, ” reports lead tester Justin Simoni. When temps drop deep, check out the Mons Royale Cascade Merino Flex Legging, which will wear a little warmer, but don't tip the scales all that much more using 180 g/sm fabric rather than 125 g/sm of the Boulder 125's. The Mons Royal also adds a fair bit of spandex to their wool-nylon blend, adding stretch to strengthen the wool where it is most delicate. The 150 g/sm Smartwool Classic All-Season Merino Bottom also utilizes wool fabric with a nylon core, but their fit isn't quite as slim as the Boulder 125s. These are really technical long bottoms, and the price for such a luxe pair of long underwear is predictably higher than other options. Yet with the Artilect Boulder 125, you get what you pay for. If durability concerns you, try out the Patagonia Capilene Midweight Bottoms instead, as they side-step the wool's problem of low abrasion resistance with a fully synthetic design that comes in at a lower price.

For colder conditions, reach for the Smartwool Classic Thermal Merino Bottom instead.

Read more: Artilect Boulder 125 review

We found that the Artilect Boulder 125 dries super quick on the line, and a nice breeze only speeds things up.
Credit: Justin Simoni

Best Midweight Long Underwear for Men


Minus33 Kancamagus Midweight Merino Wool Bottoms


73
OVERALL
SCORE
  • Warmth 9.0
  • Breathability 7.0
  • Comfort and Fit 7.0
  • Durability 6.0
  • Drying Speed 6.0
  • Layering Ability 7.0
Materials: 100% Merino wool | Weight: 8.9 oz (size Medium)
REASONS TO BUY
Plush 100% Merino wool
Secure ankle cuffs and high waist
Good value
REASONS TO AVOID
More delicate than any synthetic
Longer dry times
Not as breathable in warm weather

Midweights are our favorite for cold days and nights. If you are looking for a pair of long underwear to help keep you warm in wintry conditions above all else, the Minus33 Kancamagus Midweight Merino Wool Bottoms is a pair you should seriously consider. One of our favorite midweights, these are expertly structured, featuring 235 g/sm, 100% Merino wool with smooth, low-profile flatlock seams to fit the body almost perfectly. Our lead tester notes, “I wouldn't suggest wearing too thick of thermal underwear in all but the most extreme conditions, but these are a great choice when you know a storm is brewing.” We reach for these bottoms when a cold front is forecasted to hit, as we found they provide good thermoregulation in more frigid climes. Plus, the soft, smooth fabric is extra comfortable next to the skin and won't catch on your outer layers.

Like other 100% Merino bottoms, the Minus33 Kancamagus Midweights require a little more tender loving care, especially when they are all between you and a moment of backcountry exposure. Washing and drying can be the time when damage happens. As with any wool, consider washing them sparingly. They won't hold onto odor like other materials and can be worn many times before genuinely needing a good wash. All Merino wool bottoms can be damaged by abrasive rocks, brush, or the like, and these are no exception. The Kancamagus leggings are also just too warm for milder conditions, so bringing along a more appropriately light pair in the summer may be best. The REI Co-op Merino 185 Bottoms is an excellent choice for summertime when you still want an appreciable amount of warmth, as their 185 g/sm weight makes for a better all-rounder. If the Kancamagus is too delicate and expensive for your blood, look at a synthetic pair, like the REI Midweight Bottoms, that can take far more abuse.

Read more: Minus33 Kancamagus Midweight Merino Wool Bottoms review

The Minus33 Kancamagus Midweight Merino Wool Bottoms are a pair of bottoms we'd seriously consider bringing along for a cold alpine night in a bivy sack.
Credit: Justin Simoni

Our Favorite 3/4 Length


Smartwool Intraknit Thermal Merino 3/4 Bottom


72
OVERALL
SCORE
  • Warmth 7.0
  • Breathability 7.0
  • Comfort and Fit 7.0
  • Durability 8.0
  • Drying Speed 5.0
  • Layering Ability 9.0
Materials: 54% Merino wool, 43% polyester, 2% elastane, 1% polyamide | Weight: 9.2 oz (size Medium)
REASONS TO BUY
Seamless panels provide better warmth, ventilation, and articulation
Nice thick waistband
3/4 length helps with keeping your wearables tidy by your ankles
REASONS TO AVOID
No fly may be a dealbreaker
Athletic fit may not be for everyone

We're not shy about our love affair with Smartwool's Intraknit technology, and it's a big reason why the Smartwool Intraknit Thermal Merino 3/4 Bottom landed in the winner's circle. The seamless panels found throughout blend different fabrics to clothe you in a bottom that's warm yet well-ventilated in exactly the right places. For example, the gusseted crotch fabric facilitates perspiration to leave your body, while the fabric on the knees promotes articulation. All this in a tight, athletic fit with a high waist held up by a chunky waistband. If you prefer to be hugged tightly by your thermal bottom as you move, these are for you.

What's not to like? If an almost compression level of tightness isn't your thing, you won't fall in love with the Intraknit Thermal Merino 3/4 Bottoms as we have. Look at the Minus33 Kancamagus Midweight Merino Wool Bottoms for a pair of high-quality wool bottoms with a looser fit. The lack of a fly in the Intraknit Thermal 3/4s may also dissuade some consumers from purchasing these bottoms. “I prefer no-fly myself, but if easy access under multiple layers is a requirement, that will be a dealbreaker,” shares Justin Simoni, our lead reviewer. The Ortovox 185 Rock'N'Wool Short Pant is another 3/4 length option that coincidentally comes without a fly. You will find a fly in the similarly weighted REI Co-op Merino 185 Bottomsif it matters. Intraknit tech does put a heavy dent in the wallet, and their polymath fabrics make this pair a little heavier than other options in our review. If ultimate warmth performance is of the utmost importance to you, there are better choices (available in full-length form), but we love these 3/4 leggings for many applications. If you prefer a snug-fitting layer versus a compression tight, the REI Co-op Midweight Bottoms offer a comfortable four-way stretch at an extremely reasonable price.

Read more: Smartwool Intraknit Thermal Merino 3/4 Bottom review

We don't regularly get to try out washing our warm long underwear underneath a raging waterfall, but we couldn't help giving a try with the Smartwool Intraknit Thermal Merino 3/4 Bottoms. This pair probably benefits from hand washing, and always being hung out to dry.
Credit: Justin Simoni

Excellent Value for Cold Winter Days


Meriwool Merino 250 Bottom


67
OVERALL
SCORE
  • Warmth 8.0
  • Breathability 6.0
  • Comfort and Fit 7.0
  • Durability 6.0
  • Drying Speed 6.0
  • Layering Ability 6.0
Materials: 100% Merino Wool | Weight: 7.9 oz (size Medium)
REASONS TO BUY
Good performance at a great value
Super warm 100% Merino wool
Wide range of available sizes
REASONS TO AVOID
Not as comfortable as more paneled construction
Run slightly small

Making 100% Merino Wool apparel approachable for the masses is the Meriwool Merino 250 Bottom. We appreciate these affordable leggings' no-nonsense construction and super plush, cozy, 100% Merino wool fabric. High-end features like an extra-comfortable waistband and well-thought-out ankle cuffs will make you double-take on the extremely fair price. These are excellent thermal bottoms to wear when temperatures really start to dip down. A wide range of sizes is available to accommodate a broad range of shoppers' needs, which is something of particular note since not everyone looking to stay warm is also a super-athlete. It's great that Meriwool offers the Merino 250s in many sizes.

Aside from the overall warmth and the value of getting a 100% Merino wool bottom at a steal of a price, there is not a whole lot about these bottoms that makes them stand out among the competition. If you need a lot of features or a more technical performance out of your long under, you will want something like the Smartwool Intraknit Thermal Merino 3/4 Bottom. But that's the Meriwool's charm: they're working behind the scenes (or underneath your pants) to ensure you stay comfortable in the cold without needing a bunch of fanfare. We should note there may be a wash-in period to get the ultra-fine Merino wool to soften up a smidge. So, if you find the Merino 250 Bottom to be somewhat itchy when you first wear them, be sure you wash them before bestowing your final judgment. If you'd rather go with a comfier option, we like the feel of the Smartwool Classic All-Season Merino Bottom, which blends wool and stretchy nylon. If money is no object, for pure comfort in casual settings, you can't beat the synthetic Arc'teryx Rho Heavyweight Bottoms.

Read more: Meriwool Merino 250 Bottom review

The Meriwool Merino 250 Bottoms fit comfortably - not too tight or loose - and are a great way to add major warmth to your layering system without breaking the bank.
Credit: Justin Simoni

Compare Products

select up to 5 products to compare
Score Product Price
81
Arc'teryx Rho Heavyweight Bottoms
Best Synthetic Long Underwear for Men
$120
Editors' Choice Award
76
Smartwool Classic Thermal Merino Bottom
Best Overall Long Underwear for Men
$115
Editors' Choice Award
74
Artilect Boulder 125
Best Lightweight Long Underwear
$120
Top Pick Award
73
REI Co-op Midweight Bottoms
Best Synthetic Bang for the Buck
$55
Best Buy Award
73
Minus33 Kancamagus Midweight Merino Wool Bottoms
Best Midweight Long Underwear for Men
$80
Top Pick Award
72
Smartwool Intraknit Thermal Merino 3/4 Bottom
Our Favorite 3/4 Length
$120
Top Pick Award
70
Patagonia Capilene Midweight Bottoms
$89
69
Outdoor Research Alpine Onset Bottoms
$99
68
Ortovox 185 Rock'N'Wool Short Pant
$100
68
Mons Royale Cascade Merino Flex Legging
$120
67
Meriwool Merino 250 Bottom
Excellent Value for Cold Winter Days
$60
Top Pick Award
67
REI Co-op Merino 185 Bottoms
$80
67
Icebreaker Merino 200 Oasis Bottoms
$105
66
Merino.tech Bottoms
Our Favorite Merino Wool on a Budget
$59
Best Buy Award
64
Smartwool Classic All-Season Merino Bottom
$90
62
WEERTI Thermal Fleece Lined Set
$30
60
Thermajohn Thermal Fleece Lined Set
$40
56
Amazon Essentials Set
$21

long underwear men - river trips down the colorado river are a great testing ground for...
River trips down the Colorado River are a great testing ground for long underwear bottoms.
Credit: AJ Wojtalik

Why Trust GearLab


We take a two-pronged approach while testing men's long underwear. One side involves a lab setting where we performed specific, repeatable tests to compare each bottom with the others in the lineup directly. Metrics like durability involve our harsh abrasion test and repeated washing and drying. Warmth and breathability tests are done in climate-controlled rooms to compare all bottoms in a more standard and equal setting. The second leg of our testing journey involves taking these bottoms with us on our favorite outdoor pursuits and examining them in their natural environments. We're looking for how they perform, how comfortable they feel, how they fit, and how well they survive our abuse. These bottoms found themselves accompanying us on trips to mountain summits, off-route fastpacking, and every day on our daily bike commutes and trail runs in the hills.

We took advantage of the spin bikes at our local gym to don our toasty selection of long underwear — often at the bemusement of our gym buddies — to gauge characteristics like warmth and breathability in a controlled setting.
Credit: Justin Simoni

Our testing of long underwear is designed to cover six rating metrics:
  • Warmth (25% of total score weighting)
  • Breathability (20% weighting)
  • Comfort and Fit (20% weighting)
  • Durability (15% weighting)
  • Drying Speed (10% weighting)
  • Layering Ability (10% weighting)

Our expert on cold weather-layering systems is Justin Simoni, a Boulder, CO-based athlete, adventurer, and backpacking guide. He specializes in ultra-long distance, self-powered, and self-supported challenges in the mountains of the American West. Many of those challenges see him gain and lose thousands of feet of elevation, so his layering systems have become finely tuned. He has worked closely with outdoor gear companies for over a decade, bringing his experience and equipment expertise to the table.

Justin is joined by Aaron Rice. Pursuing snowy adventure as a way of life, Aaron works as a ski patroller, avalanche educator, and snow scientist —- ask him about stellar dendrites or the finer aspects of back-door cold fronts, and he'll gladly talk your ear off. In his free time, you might chance across him in the seldom-traveled high mountains of New Mexico while out trail running, backpacking, alpine climbing, and ski touring.

Field testing the Smartwool Merino 250 bottoms, now called the...
Field testing the Smartwool Merino 250 bottoms, now called the Classic Thermal.
Side-by-side testing is our bread-and-butter. Here, we compare the...
Side-by-side testing is our bread-and-butter. Here, we compare the fat waistband of the Ortovox 185 Rock'N'Wool with the thinner waistband of the Outdoor Research Alpine Onset bottoms.
Long underwear bottoms are a versatile addition to your outdoor...
Long underwear bottoms are a versatile addition to your outdoor collection.
Our team of intrepid adventurers took out these pairs of long underwear on their travels to test their mettle and shake out which ones are the very best for you.

Analysis and Test Results


Long underwear (commonly called base layer bottoms or thermal underwear) keeps you warm and regulates your body temperature while you're out playing in colder conditions. Base layer bottoms often only get pulled out when the cold of winter sets in, but even if they aren't used as frequently as tops, they can still be quite versatile. You can pack them as pajamas on a backpacking trip, have them pull double-duty as cold-weather running tights, or just layer them under your favorite pair of jeans for a night around a bonfire. They become necessary when tackling cold-weather activities like ice climbing and skiing. Regardless of the situation, these bottoms keep you dry and comfortable by wicking sweat away from your body, improving thermoregulation and your outdoor experiences.

long underwear men - grab a bottom base layer once the flurries start to fly!
Grab a bottom base layer once the flurries start to fly!
Credit: Justin Simoni

We design our field and laboratory testing to be comprehensive and mutually exclusive. We determine scores for each metric, compile those numbers, and assign a total score for each pair. It is important to note that the assigned scores are determined relative to the other products in the review. We specifically test only the best layers on the market, so a low score does not mean that a product is not worth its weight-in-wool — it simply means that it does not perform as well as other products when compared side-by-side. By testing and rating each of these layers relative to one another, we can highlight specifics to inform your next purchase.


What's the Best Value?


Though it may come as a surprise, some of these bottoms are expensive. If you're a mountaineer, go on multi-day ski tours, love winter camping, or just spend a lot of time working or recreating in cold conditions, investing in a high-end, performance-based layer is easier to justify. However, if you're just looking for a pair to pull on to shovel the sidewalk, you likely have some more wiggle room and can still get your hands on a decent-quality product for a lower cost.

long underwear men - these ortovox woolies are exceptional, but may just be too much long...
These Ortovox woolies are exceptional, but may just be too much long underwear for what you need.
Credit: Justin Simoni

Merino wool models, in general, will cost more because the material is more expensive to produce. However, you help offset external costs by opting for an all-natural product. Synthetic models are almost always less expensive and often carry quick-drying capacity, which can be very important when the weather begins to warm up. Despite the environmental costs of production, synthetics tend to be more durable than Merino, lasting through many wash cycles, so their longevity adds to their value.

For those needing a warm pair of bottoms at a great price, consider the REI Co-op Midweight. For the sustainably-minded, the Patagonia Capilene Midweight Bottoms is a synthetic option made from 100% recycled polyester. For wool, the Meriwool Merino 250 Bottom and Merino Tech Bottom buck the trend of wool being super expensive and are great introductory pairs to the world of wool.

long underwear men - some bottoms spell it out for you, like these capilene midweights, a...
Some bottoms spell it out for you, like these Capilene Midweights, a base layer that is clearly designed for “cool to cold” conditions - most times we're not so lucky with up-front information on the tag.
Credit: Jill Rice

Warmth


Warmth is one of the most important factors when shopping for long underwear. The success of a layer in keeping you warm is rooted in its ability to trap your body heat in the fabric fibers while wicking sweat away from your body, keeping you dry and comfortable even while active. Thicker materials often correlate to a warmer base layer, but the fabric type and fit can also impact how breathable and comfortable the thermal underwear can be.


Base-layer bottoms are versatile, but warmth is a dynamic metric; we don't all run at the same temperature. When considering a pair of bottoms, consider how you plan to use them. We've worn these layers while working up a sweat while skinning steep terrain, walking the dog in freezing temperatures, backpacking in the fall, and sleeping in the back of a truck or out in a tent through the long, dark, cold nights.

We test warmth in the lab by working up a sweat and seeing how much of the heat we produced is retained by the bottoms.
Credit: Justin Simoni

Do you want versatility across all four seasons or just mid-winter warmth? Are you layering them under a single, technical pair of hardshell climbing pants or a thick pair of ski pants that already offer a degree of warmth and insulation? It is important to know that the warmest bottoms aren't always the most practical.

long underwear men - the smartwool intraknit thermal merino 3/4 bottoms were great on...
The Smartwool Intraknit Thermal Merino 3/4 Bottoms were great on wintry hikes - the 3/4 length works well when paired with thick warm socks, preventing too much overlap.
Credit: Justin Simoni

If you're looking for a more versatile pair of long underwear, the REI Co-op Midweight Bottoms and Ortovox 185 Rock'N'Wool Short Pant are midweight options that tend to blend the seasons. If warmth isn't as pressing for you, a lightweight option like the Outdoor Research Alpine Onset Bottoms, REI Co-op Merino 185 Bottoms, and Patagonia Capilene Midweight may be the ticket for summer backpacking, cross-country skiing, or winter climbing trips to the desert. Similarly, if you're looking for a lightweight layer for your SkiMo training, the Artilect Boulder 125 relies upon moisture-wicking capability more than warmth by insulation alone.


Need bottoms for activities in the bitter cold? Seek out thick, 100% Merino wool bottoms, which our tests reveal retain the most heat. The Smartwool Classic Thermal Merino, the Minus33 Kancamagus Midweight Merino Wool Bottoms, the Meriwool Merino 250, and the Merino Tech Bottoms are all excellent choices.

A magnified view of the Smartwool Classic Thermal Merino Bottom's...
A magnified view of the Smartwool Classic Thermal Merino Bottom's 100% merino wool knit
A magnified view of the Meriwool Merino 250 Bottom's 100% merino...
A magnified view of the Meriwool Merino 250 Bottom's 100% merino wool knit
A magnified view of the Minus33 Kancamagus Midweight Merino Wool...
A magnified view of the Minus33 Kancamagus Midweight Merino Wool Bottoms's 100% merino wool knit
The Merino Tech Bottoms seen under a microscope.
The Merino Tech Bottoms seen under a microscope.
These magnified samples of 100% Merino Wool bottoms reveal their knit construction.

Need winter-level warmth but don't want to go the wool route? Your options may be limited, but the Arc'teryx Rho Heavyweight Bottoms are an excellent synthetic choice with a heavily insulating yet soft next-to-skin interior and an outer layer that's sheerer and won't catch on your exterior pants layered above.

The synthetic fabric of the Arc'teryx Rho Heavyweight Bottoms have two different fabric faces: one to trap warm around; the other to glide easily against other layers.
Credit: Justin Simoni

Breathability


Breathability is a quality that can make or break the effectiveness of a base layer when it comes to regulating body temperature. A garment's ability to breathe lives in the fibers of the fabric. Breathability is the fiber's capacity to move heat-induced moisture (i.e., sweat) from the inside of the garment to the outside, allowing it to evaporate from the surface of the layer. This process keeps you from overheating and lets your bottoms dry out continuously, even when you're sweating. Improved breathability keeps you from becoming a soggy mess, ultimately keeping you warmer in cold temperatures.


Our body temperature doesn't fluctuate as intensely on our bottom half as on our top half. But it does house some of our major working muscles and thus is an area good at producing consistent heat. Having a pair of long underwear that will dump heat and stay dry is important when participating in highly aerobic, start/stop activities like backcountry skiing. Not so shockingly, the most breathable layers we tested are lighter in terms of their fabric weight.

long underwear men - there's snow somewhere around here, we just know it! putting...
There's snow somewhere around here, we just know it! Putting breathability to the test on a much too warm and dry day to be hiking in ski bottoms.
Credit: Kricket Servis

Almost every Merino wool layer we tested offers superior moisture-wicking ability. This is a natural quality of Merino wool, allowing these layers to breathe while you're on the move. If you are seeking a high level of breathability from a full Merino pair of long underwear, the Smartwool Classic Thermal and Ortovox 185 Rock'N'Wool are great choices.

long underwear men - feel wild and free when your bottoms feature great breathability,
Feel wild and free when your bottoms feature great breathability,
Credit: Justin Simoni

While all-natural fibers dominate in terms of wicking ability, synthetics tend to dry faster on the body. The Patagonia Capilene Midweight is a full synthetic bottom that does a solid job of wicking away moisture. The Thermajohn Thermal Fleece Lined Set and WEERTI Thermal Fleece Lined Set also do a good job with breathability, as their fabrics are quite thin.

long underwear men - the perforated fabric of the patagonia capilene midweight do an good...
The perforated fabric of the Patagonia Capilene Midweight do an good job breathing well while wicking away moisture.
Credit: Justin Simoni

The front runner in this metric is the Artilect Boulder 125, which uses an 85% Merino wool and 15% nylon blend to produce a thin 125 g/m² fabric that's super breathable while staying relatively durable. The Ortovox 185 Rock'N'Wool Short Pant uses a super soft and lofty 185 g/m² to perform well in both breathability and warmth.

long underwear men - the artilect has great breathability, perfect for active wear.
The Artilect has great breathability, perfect for active wear.
Credit: Justin Simoni

The Mons Royale Cascade Merino Flex Legging also scores admirably in this metric. The Merino-blended fabric seems thinner than its advertised 180 g/m², resulting in a lighter-weight pair of bottoms than we expected. They also have an athletic fit, hugging tightly around your legs, which helps transfer moisture away from your skin.

long underwear men - the mons royale cascade merino leggins are thin, very stretchy...
The Mons Royale Cascade Merino leggins are thin, very stretchy, highly breathable, and feature a thick, comfortable waistband.
Credit: Justin Simoni

Cotton-based long underwear doesn't score too strongly compared to far more expensive wool, nor does it compare well with many synthetics when wet. Still, if kept relatively dry, the Amazon Essentials Set showed good results using our air permeability tests.

long underwear men - although not the warmest of long underwear, the 60% cotton, 40%...
Although not the warmest of long underwear, the 60% Cotton, 40% Polyester Amazon Essentials Set are certainly breathable.
Credit: Maddock Rigby

Comfort and Fit


Comfort is a reasonably uniform metric across different users — we all want to wrap our legs in plush, soft-spun wool or silk-like polyester. But the fit is very much subjective, as “perfection” understandably varies just as much as we vary in body type. Through analysis of articulation, seam placement, cut, and design features, we do our best to identify any areas of concern that may apply to every user, not just those that match our bodies. But that said, we always suggest trying clothing on in person so you can decide if it fits well.


We consider several factors to determine comfort and fit:
  • Feel of the fabric next to the skin
  • How tight or loose they fit in particular zones, such as the knees and cuffs
  • The stretch of fabric and freedom of mobility
  • Width and comfort of the waistband
  • Length of the legs and fit of the cuffs
  • Depth of the crotch, factoring in any bottom-sag
  • The type of seam stitch, articulation, and the associated comfort of the type of stitch used

Having our collection of different long underwear to try and compare in succession really helps reveal how each one feels and fits differently.
Credit: Justin Simoni

We only test high-quality products here, so comfort is fairly uniform. But when it comes to ranking pairs of long underwear side-by-side, the fit sets them apart. If you are looking for that ultra-soft pair, perfect for getting after it or just hanging out and relaxing, check out the Smartwool Classic Thermal Merino and their lighter weight brethren, the Classic All-Season.

long underwear men - the artilect boulder 125s are made of nuyarn: a merino wool spun on...
The Artilect Boulder 125s are made of Nuyarn: a Merino wool spun on a nylon core. This makes them as comfortable as Merino but as stretchy as a synthetic layer
Credit: Justin Simoni

Many bottoms mix synthetic fibers with wool to add a long-lasting stretch that hugs the body. This material is found in the uber comfy Smartwool Intraknit and Artilect Boulder 125. We adore the extra wide waistband of the Mons Royale Cascade Merino Flex Legging, which we found distributes the band's pressure around a wide area.

long underwear men - the intraknit tech in the smartwool intraknit thermal merino 3/4...
The Intraknit tech in the Smartwool Intraknit Thermal Merino 3/4 Bottom certainly did impress on when it come to the stretch and movement of the panels found on areas of the bottoms, such as the knee.
Credit: Justin Simoni

It's hard to argue against a pair of long bottoms that feel like luxurious, insulated leggings, but in a sense, that's what the synthetic Arc'teryx Rho Heavyweight Bottoms are. If you're not hitting the slopes with these under your ski pants, they're just as excellent lounging around the hotel sipping on cocoa.

long underwear men - quality time with our best friend in our comfiest clothes is what...
Quality time with our best friend in our comfiest clothes is what makes Winter one of our favorite seasons!
Credit: Maddock Rigby

Durability


Durability has never been a particularly strong suit for base layers -— remember, these bottoms are specifically designed to be worn at the base of your kit. When these layers can pull double duty as a pair of running tights, we like to think of it as more of a bonus than a requirement.


Merino wool is historically susceptible to rips, tears, and punctures, but brands have made serious strides in recent years to enhance the durability of this all-natural fiber. For example, Smartwool uses a process that wraps the Merino wool around a nylon core to increase durability, which makes the Intraknit Thermal Merino particularly durable for its weight. The Artilect Boulder 125 does a similar thing, using Nuyarn instead of a proprietary blend. The Outdoor Research Alpine Onset is a polyester-wool blend that teases both materials' benefits into one.

long underwear men - durability is key for pair of long underwear to last on multi-day...
Durability is key for pair of long underwear to last on multi-day trips.
Credit: Jill Rice

While wool-synthetic blends are improving, the most durable pairs of long underwear we tested are still synthetic. The REI Co-op Midweight Bottoms scored extremely well in durability, thanks to their hardened yet comfy four-way stretch fabric. Another synthetic bottom, the Patagonia Capilene Midweight, is almost as durable considering the thinner makeup of the fabric.

long underwear men - durability of the rei midweight bottoms is excellent as the...
Durability of the REI Midweight Bottoms is excellent as the synthethic fabric resists abrasions. The snug fit and four way stretch of the fabric survived our repeated washings.
Credit: Justin Simoni

Drying Speed


We test and report on drying speed for a few important reasons. First and foremost, many materials used in these base layer bottoms can't be thrown in the dryer with your everyday clothes. Wool tends to shrink and lose shape in addition to shedding fibers, making this the quickest way for it to meet an early grave. Even 100% Merino wool bottoms and most synthetics utilize elastane in their waistband, not to mention the fabric itself, which also degrades with drying. We suggest drying your long underwear on the line or laying the underwear flat to dry. Secondly, on-the-line drying speed can indicate how fast the bottoms will dry out when you're wearing them, which also correlates with breathability.


Lighter-weight fabrics of all threads will dry faster on the line than heavier fabrics. The WEERTI Thermal Fleece Lined Set and Thermajohn Thermal Fleece Lined Set dried at breakneck speeds due to the lightweight, synthetic fabric they're constructed from. We did notice the start of some pilling in both of these, so it is best to dry these out on the line rather than in the dryer.

We were surprised at how fast some heavier bottoms in our test group dried out. The Icebreaker Merino 200 Oasis Bottoms had excellent drying speed performance for their weight, as did the 3/4 length Ortovox 185 Rock'N'Wool Short Pant. The Arc'teryx Rho Heavyweight Bottoms dazzled us with how fast they dried, especially compared to the midweight woolen options that occupy the same cold weather niche. Consolation prizes go to the Patagonia Capilene Midweight, our fastest synthetic dryer, as well as the Artilect Boulder 125 and Mons Royale Cascade Merino Flex Legging, which dried out quickly due to their overall svelteness on the scale.

long underwear men - the icebreaker oasis 200 dries impressively fast, especially...
The Icebreaker Oasis 200 dries impressively fast, especially considering their weight.
Credit: Justin Simoni

Layering Ability


What's the point of a good pair of bottoms if they don't pair well with anything else you own? This metric judges how well these long underwear work within your clothing system. We look at various factors: does the manufacturer use features like low-profile flatlock seams to reduce chafing? Does the waistband keep the bottoms up, and are the leg cuffs adequate to keep them down? A front fly can add convenience, but a lack of fly may mean you can wear these bottoms au naturel - a nice extra benefit. A tighter fit can also help outer layers slide easily over the top.


The Smartwool Intraknit Thermal features a tight, compression-like fit, and the 3/4 length we tested helps prevent the bunching up of your socks above the ankles. The Outdoor Research Alpine Onset Bottoms and the REI Co-op Merino 185 Bottoms also fit close-to-skin, with fabric that easily slides over mid and outer layers.

long underwear men - grab a versatile pair of long underwear bottoms, like the outdoor...
Grab a versatile pair of long underwear bottoms, like the Outdoor Research Alpine Onset bottoms, and set out for your next adventure!
Credit: Jill Rice

How to Choose a Men's Long Underwear



long underwear men - get your base and long underwear choices dialed in for your perfect...
Get your base and long underwear choices dialed in for your perfect laying system.
Credit: Justin Simoni

When temps start to dip down, it's time to think about getting a pair of long underwear to supplement the warmth your outer layers may provide. But choosing just the right pair may seem daunting, with so many options now available.

Does the type of fabric make a difference?


One of the biggest differences across long underwear options is the type of fabric they're made out of. Almost all the long underwear in our lineup are either made of wool, a wool blend, polyester, or a cotton blend. Each has its advantages.

long underwear men - it's hard not to get excited by a new pair of wool long bottoms!
It's hard not to get excited by a new pair of wool long bottoms!
Credit: Justin Simoni

Wool


Wool is soft, feels great in hand, and has exceptional insulating properties and breathability. It even performs well when wet, staying warmer than other fabric types. Although an exceptional material, it can also be the most delicate, both while wearing and washing. It can also be one of the most expensive.

Wool blends attempt to improve many shortcomings associated with 100% wool fabrics. Polyester is usually added to the wool fiber to enhance its strength and even to provide a little more stretch to the fabric. Blends can add more value to your pair of long underwear but don't necessarily help with the cost.

long underwear men - polyester bottoms are a great choice for long underwear, especially...
Polyester bottoms are a great choice for long underwear, especially since durability is even more important when compared to tops.
Credit: Justin Simoni

Polyester


Polyester pairs can have a huge “leg up” to their wool counterparts when it comes to durability, as a polyester fabric can be knitted with a strength that far exceeds that of wool at the same weight. You'll give up a little in absolute warmth and perhaps comfort, but usually, the price of a polyester bottom makes them very attractive, especially in the mid and lightweight subcategories, where a wool pair may prove too delicate to wear for most.

long underwear men - long underwear made with a cotton blend can give some benefits at a...
Long underwear made with a cotton blend can give some benefits at a great price, but may not give the performance you may desire for outdoor adventures.
Credit: Justin Simoni

Cotton Blends


Although less appropriate for outdoor activities, cotton-blended fabrics make cozy options perfect for lounging around and tackling low-output activities like dog walks on winter days, and they're usually priced as a budget item with a performance to match. These will do the job if you need just a simple pair of long bottoms for more casual use. But they are not advisable for outdoor pursuits given how highly absorptive cotton can become, leaving you wet, cold, and miserable — a dangerous combination when exposed to the elements. If you are heading up Denali mid-winter or skiing amid the Rockies on a spring day, skip the cotton and pick up something in wool or synthetic that is sure to be moisture-wicking and quick drying.

long underwear men - in the shoulder season, it's great to have a pair of long bottoms...
In the shoulder season, it's great to have a pair of long bottoms for insulation, but they don't always have to be super thick and heavy.
Credit: Justin Simoni

What Are The Insulation Weight Classes About?


Generally, long underwear can be categorized by weight: “lightweight,” "midweight," “heavyweight,” etc. The heavier the weight of the fabric, the more insulation the bottoms have. If you're going to be in bitterly cold conditions, you'll want to pick out a pair of long underwear that's on the heavier side of things. But if you're just looking for a pair to wear while sleeping out on a backpacking trip during the summer, you probably want to try a lighter-weight pair.

Heavier long underwear may be warmer, but you'll also find them less breathable, and typically, they will take longer to dry out. So, if you start your morning run wearing a heavy pair of long underwear, chances are you'll sweat through them before you finish your run, negating the insulative qualities of the underwear. It may be better to start with a lighter weight but more breathable pair of leggings, which may not be warmer but will more easily breathe and wick away sweat, leaving you as comfortable at mile 10 as you wear at mile 1.

long underwear men - when hanging out with our best buds, a simple and inexpensive pair...
When hanging out with our best buds, a simple and inexpensive pair of long underwear works just perfectly.
Credit: Justin Simoni

How Much Should I Spend on Long Underwear?


The best long underwear to buy isn't always the most expensive, but you want to ensure what you buy fits the purpose you're looking to fill. The least expensive pairs in our review are cotton blends that may be perfect if you only want something extra to wear at home when the temperature dips lower than usual for a few weeks. But if you regularly recreate outside, you may want to spring for a more performative pair of long underwear that wicks away moisture and breathes well while keeping you extra warm. If you're traveling in the backcountry, don't underdress to save a few dollars and then need to call Search and Rescue!

Some of the most expensive pairs in our lineup are made of wool and wool blends, as wool is an expensive material. Yet it offers excellent performance, especially when assessed for the warmth it provides. Polyester fills an excellent middle ground, being a good choice for all but extreme conditions. You might consider using a polyester bottom when absolute performance isn't necessary. Cotton blends, as we've noted, are for more casual uses only and are not a safe bet to keep you warm on outdoor adventures. But they can be a good choice if budgets are very tight and you need something for around town — just understand that they come with very real safety limitations.

Conclusion


For work and play, long underwear bottoms are a great way to extend your seasons and help keep you outside through the coldest months of the year. When hunting for your next perfect pair, it is important to consider your temperature disposition and how and when you plan to use them. In our testing, we sought out different climates to determine which pairs are best for warmer seasons and which are best to wear through the coldest depths of winter and found that the set you choose does make a difference. From all-day ski tours to desert backpacking trips to shoveling the driveway and hanging on the couch, these versatile bottoms will keep you warm and dry no matter the activity or occasion.

long underwear men - where will your next pair of long undies take you?
Where will your next pair of long undies take you?
Credit: Justin Simoni

Justin Simoni and Aaron Rice