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We've tested over 100 pairs of the best long underwear for men and women from brands like Ridge Merino, Smartwool, Patagonia, Black Diamond, Icebreaker, REI, and more.
The Eastern Sierra is certainly a beautiful place for testing the drying speed of every pair of long underwear.
When temps drop low, but life still has you heading outside, it's time to layer up. And the best, most effective thermal systems will always start with a reliable base, including a great pair of long underwear.
Our testing teams have spent more than a decade hunting for the best of the best among base-layer bottoms. We've carefully examined top sellers for both genders, identifying the strengths and weaknesses within each design and subjecting each pair to a mix of demanding backcountry missions and winter chores at home. This extensive testing allows us to objectively evaluate each bottom's thermal performance side by side, so we can now provide you with a highlight reel of our favorites.
Because we understand the foundation of your cold weather performance kit can affect your backcountry experience and may even become your go-to for cozy nights during the dark and cold months of winter, we've also done the hard work to evaluated the best base layers and our favorite ski jackets and ski pants — and even warm socks to keep you comfortable indoors and out all winter long.
It was easy for us to give top honors to the Smartwool Classic Thermal Merino Bottom thanks to their high-performing 100% Merino wool construction. These bottoms supply top-notch warmth and a welcoming softness against the skin, especially when the temperatures drop. The uniquely crafted interlocking knit maintains breathability even within its thick 250 g/m² fabric weight. The extra-wide wool-lined waistband, along with front and back gussets, increases the comfort and mobility of these bottoms. Flat lock seams also contribute to comfort and reduce complaints regarding itchy fabric. Our leader tester noted, “Although these are designed specifically with cold weather in mind, I find them versatile enough to be worn throughout the year thanks to the exceptional thermoregulation they provide.”
SPECIFICATIONS
Insulation Weight Class
Midweight
Material
100% Merino wool
Measured Weight (Size Medium)
8.3 oz
Measured Inseam (Size Medium)
31.0 in
Although the Classic Thermal Bottoms are some of the thickest and most durable all-natural bottoms we've tested, Merino wool requires another level of care compared to its synthetic competition. Lead tester Simoni reminds us that Merino is delicate, and such bottoms are susceptible to damage, noting, “I find their lifespan is greatly reduced when not properly cared for.” So, rather than throwing them in the dryer, we'd recommend laying them flat to dry if you want them to enjoy a full lifespan. That being said, this 100% Merino wool design doesn't have any elastane or spandex to help control its shape, which can be unappealing to some wearers since they are prone to stretching between washes. A high-quality base layer is an investment; such natural fibers don't generally come cheap. If special care instructions sound daunting and you'd prefer to save money, we recommend the REI Co-op Midweight Bottoms for their affordable yet noteworthy synthetic performance. Or for a more budget-friendly Merino wool option, the Meriwool Merino 250 Bottoms are another thick wool design that provides solid performance across a range of testing metrics.
The Icebreaker 200 ZoneKnit Merino Leggings quickly became the bottoms we found ourselves reaching for the most, thanks to their extraordinary 100% Merino wool construction. Lead tester Trish Matheny described these as “The pair I grab whenever I am headed out to the backcountry, and I know there will be cold nights ahead.” These are true to size and made of a soft, stretchy, ultrafine 200 g/m² fabric that sits close to the skin. Tightly woven sections are combined with carefully placed body-mapped ventilation panels to increase the natural wicking performance and breathability of the Merino wool. This is the fourth iteration of the ZoneKnit design, and thoughtful details we found include a gusseted crotch to enhance mobility and flatlock seams to eliminate any points of discomfort while ensuring a longer lifespan for the bottoms. For anyone who wants a little thicker fabric weight, we recommend the Icebreaker 260 ZoneKnit Merino Leggings.
SPECIFICATIONS
Insulation Weight Class
Lightweight
Material
100% Merino wool
Measured Weight(Size Small)
5.63 oz
Measured Inseam Length (Size)
27.5 in (small)
Although we only encountered minimal signs of wear and tear within the perforated, ventilated panels on the bottom of the Icebreaker 200 ZoneKnit Leggings, there's no doubt these Merino wool bottoms are delicate. They may not be the ideal choice for everyday use. If durability is a primary concern, we'd recommend the SmartWool Intraknit Thermal Merino Bottoms, which are primarily a Merino wool design but also incorporate a good amount of polyester and elastane to increase their long-term durability. That thicker, more rigid fabric, in turn, sacrifices some breathability and softness, but for heavy everyday wear, that may be an acceptable exchange. However, for winter athletes, after a highly breathable design suited to high output cold weather activities, the 200 ZoneKnit is tough to beat. That said, our tester reminds us, “I do not recommend these for relaxed, low-output winter days, since their enhanced breathability undermines the warmth they offer if you are not actively on the go.” For sedentary warmth, look at the Ridge Merino Inversion Heavyweights that are perfect for cold weather days on the chairlift. Caveats aside, the 200 ZoneKnit bottoms stand out for their high-performing, versatile design suited for year-round use.
The Icebreaker 200 ZoneKnit bottoms were created with breathability and ventilation in mind. Despite their 100% Merino wool construction they dry quickly due to the perforated ventilation panels.
If you're after one of the warmest synthetic long underwear options available today, you should put the Arc'teryx Rho Heavyweight Bottoms on your list. These heavyweight bottoms supply a fit that's true to size, resembling a tight pair of joggers but with the added capability of locking in body heat generated during active pursuits. These are also great choices for those seeking an alternative, non-wool option comparable in warmth to a thick wool thermal bottom, like the Smartwool Classic Thermal Merino Bottom. However, they won't offer the same top-notch thermoregulation that Merino options can. “These are the long bottoms I grab when I want to supplement my wardrobe with some serious warmth.”, says our lead reviewer. Their design incorporates a sheer, smooth outer face that is thick and durable enough to protect the soft and plush interior face, which feels superb next to the skin.
SPECIFICATIONS
Insulation Weight Class
Midweight/heavyweight
Material
53% polyester, 38% nylon, 9% elastane
Measured Weight (Size Medium)
9.5 oz
Measured Inseam (Size Medium)
32.0 in.
Breathability is where the Arc'teryx Rho Heavyweight Bottoms suffer. Our lead reviewer calls out this design for the potential to overheat, stating, “A poor matchup is a brisk day and a fast run; I found I quickly overheated and sweat started to build up.” The Rho is an excellent choice for cold-weather performance on less active days. While this synthetic design is tough to beat, the Rho is the heaviest pair of long underwear bottoms in our lineup, and its expensive price tag may not appeal to those with a strict budget. If you're interested in a more versatile (and affordable) pair of long underwear bottoms, check out the REI Co-op Midweight Bottoms, which are available in a lighter weight, less expensive design more appropriate for year-round use. If you plan on using your long johns to work up a sweat, we recommend the Patagonia Capilene Midweight Bottoms as a more breathable alternative built for active mountain enthusiasts.
The Arc'teryx Rho Heavyweight Bottoms offer enough versatility to be layered beneath your ski bibs or worn as a stand alone legging during more mild conditions.
Delicate construction subject to durability issues
Synthetic fabric retains body odor
The Patagonia Capilene Thermal Weight leads the pack when it comes to a modern synthetic long underwear bottom that prioritizes wicking performance and breathability. But tester Trish Matheny points out, “These bottoms are not for sedentary or low-output cold-weather activities, they are built to move with you, shedding sweat and trapping essential body heat.” The design is constructed from 92% recycled polyester and 8% spandex, providing a midweight construction that can be worn throughout the year. It is not our first choice for a stand-alone legging due to the transparent sections integrated with Polartec fabric to allow air to penetrate more easily, wicking sweat while retaining heat. Synthetics often sacrifice some skin-side comfort, but this synthetic combination includes power grid fleece to provide a soft and cozy interior that's comfortable enough to sleep in.
SPECIFICATIONS
Insulation Weight Class
Midweight
Material
92% recycled polyester, 8% spandex
Measured Weight(Size Small)
4.90 oz
Measured Inseam Length (Size)
27.0 in (small)
Like most synthetics, the Thermal Weight bottoms got smelly after a few weeks of use, even with HeiQ Fresh odor control treatment. For those considering a multi-day, human-powered adventure, this could be dealbreakerer come day five of your trip. If you'd like to prioritize breathability without the stink, the Icebreaker 200 ZoneKnit Merino Leggings offer a design that's tough to beat. Like the ZoneKnit, Patagonia's Capilene Thermal Weight Bottoms aren't the best to wear alone or when just lounging around in cold temperatures due to the transparent fabric sections. Our tester points out these bottoms really shine when you need breathability, saying, “I love these for backcountry skiing, cold-weather training runs, or days in my nordic skis!” If you're interested in another synthetic bottom that is less niche and more versatile, we recommend Patagonia's Capilene Midweight Bottoms, which are available in a lighter weight that can be worn on their own. They are much more durable, though they are not equally soft nor breathabile. They also feature the same high-waisted fit found on the Therman Weights, which is flattering on most body shapes.
Our lead tester was happy to have the Patagonia Capilene Thermal Weight Bottoms during a spring ski ascent of Birch Mountain. These bottoms offered breathability all along the 7,000 foot climb while keeping us warm on that windy summit.
We're always on the hunt for a high-quality and affordable product that outperforms its price tag, and these Merino Tech Bottoms do exactly that. These soft, comfy, and incredibly warm bottoms delivered an excellent performance during testing and sell at a price that is easy to justify. “If you're looking to grab your first pair of wooly bottoms, this is an easy recommendation,” notes our lead reviewer, Justin Simoni. The tightly-woven, ultra-fine 100% Merino wool construction is paired with low profile, yet strong and effective flatlock seams to set this pair of thermal long underwear apart. Another budget-friendly option, the Meriwool Merino 250 Bottom, provides a heavier weight base well-suited to colder temperatures. At the same time, our tester found the Merino Tech Bottoms a more comfortable choice for higher-output activity on cold days. The slim fit is true to size yet doesn't limit your range of motion when training in the cold, whether running along a snowy trail or skinning up a mountain. They also do a sufficient job of wicking moisture away from the skin while trapping that hard-earned body heat.
SPECIFICATIONS
Insulation Weight Class
Midweight
Material
100% Merino wool
Measured Weight (Size Medium)
7.8 oz
Measured Inseam (Size Medium)
28.8 in
Although we've been hyping up the soft material, this delicate wool is one of the biggest drawbacks to the Merino Tech bottom's design. While the ultra-fine fibers feel great next to your skin, they don't hold up as long as their synthetic counterparts since there is no outer layer to protect them from abrasion. As with all Merino, we highly recommend following the specific care instructions provided to get the most out of your investment and extend the garment's life. While Merino Tech gives these bottoms a dryer-safe status, our test team has its reservations and still suggests drying them on the line or even laying them flat to get the most out of your investment. If you're interested in other basic, budget-friendly options for casual winter days around town, we recommend taking a look at Amazon Essentials Set and the WEERTI Thermal Fleece Lined Set. Just be aware that these options don't supply nearly the same warmth as the Merino Tech Bottoms, and cotton-blends are never safe options for outdoor activities. For an affordable bottom that supplies a thinner fabric with more versatility for year-round use, the REI Co-op Merino 185 Bottoms are a great choice.
The Merino.tech Bottoms are made from bonafide 100% merino wool and feature a delicate and tightly-woven construction that feels great next to your skin.
If you're interested in the high-quality performance of Merino wool but can't get past that expensive price tag, let us recommend the Minus33 Franconia Midweight Wool Bottoms. These midweight bottoms were among the very softest bottoms we tested, thanks to their 100% Australian Merino wool construction. The tightly woven 235 g/m² fibers are thicker and warmer than most midweight bottoms in our lineup, perfectly retaining body heat during activity. Although they feature a more traditional, stripped-down design that lacks such extras as body-mapping technology for better mobility or ventilation panels that aid in breathability, the ultra-fine, 18.5-micron Merino wool still provides ample thermoregulation and rests super softly against your skin. The looser fit also leaves room for air to permeate these bottoms and wick moisture from the skin. If a distinctly breathable performance for high activity days is what you seek, the Icebreaker 200 ZoneKnit Merino Leggings are the better choice, but for the cost, these Minus33 bottoms are a surprisingly impressive find.
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While the Franconia Midweight offers a fit that's true to size, they are looser than other midweight bottoms that we tested. The looser fit is also subject to stretching out between washes, due to the ultra-soft 100% Merino wool fabric. One tester did note, however, that “If you prefer a slimmer fit or find yourself between sizes, I think it's worth sizing down for optimal results.” You may also like the REI Co-op Midweight Tights since they have a little more stretch and give within the structure of the legging. And for those seeking a stand-alone synthetic that's also quite affordable, we've been loving the Baleaf Fleece Lined Thermal. The Baleaf is a much different bottom — it's more of an everyday tight better-suited for stand-alone use. Although the Franconia is subject to stretching, the structure can be restored with just one wash cycle. And even with a little stretch, the minimal waistband remains effective on its own or when layered beneath your ski pants. Our testing team took a chance on these inexpensive Merino wool bottoms and were pleasantly surprised by their softness, warmth, and overall performance.
The Minus33 Franconia Midweight features 100% Australian Merino Wool that is super soft next to your skin, making it the perfect foundation for cold weather layering.
The latest iteration of the REI Co-op Midweight Bottoms offers even more impressive performance within an affordable, durable, and no-nonsense pair of synthetic long underwear bottoms. Forget any of our previous criticisms of this budget long john. REI has since completely redesigned these bottoms to include 100% polyester fabric and new and improved four-way stretch to promote comfortable mobility. These are bombproof, perfect for those seeking a durable synthetic thermal bottom that can withstand everyday use. The understated and traditional cut fits close to the skin but isn't athletically tight, which we believe offers more versatility for variousody shapes and sizes. The midweight 200 g/m² constriction is the warmest midweight synthetic bottom we've tested, even giving 100% Merino wool bottoms a run for their money.
SPECIFICATIONS
Insulation Weight Class
Midweight
Material
92% recycled polyester, 8% spandex
Measured Weight (Size Medium)
7.4 oz
Measured Inseam (Size Medium)
29.5 in
We found very few weaknesses in the updated Midweight Bottoms during testing, and their overall performance is tough to beat. One tester commented, “I have little to complain about here — they are a great buy, all things considered.” That said, if synthetics aren't for you, there are several excellent Merino wool options that will do the trick. The top-tier Smartwool Classic Thermal Merino Bottoms cost nearly double what REI's Midweight will put you out, but they are among the very warmest bottoms we've tested and feel great against the skin. The Minus33 Kancamagus Midweights are more akin to the REI Midweights in price and performance in most metrics, but a bit warmer and more delicate for the extra expense. For those willing to invest in a top-performing synthetic bottom, you can't go wrong with the Arc'teryx Rho Heavyweight Bottoms — the Polartec interior rivals the comfort of wool, and the Heavyweight construction offers exceptional cold weather performance.
The REI Co-op Midweight Tights feature a blended polyester-spandex construction that delivers top-quality performance, especially considering its affordable price tag. These are notably soft next to the skin and the fabric's four-way stretch ensures unlimited range of motion. These thermal bottoms can be worn as the base of your layered system during the colder months of the year or as a stand-alone tight that supplies enough warmth for in-between seasons activities. The high-waisted design features a thick, flattering waistband and our testers found the overall fit to be true to size. Durable flatlock seams make these a great choice for everyday use, but if you're interested in an even better daily synthetic workhorse, check out the Patagonia Capilene Midweight Bottoms. Although not as stretchy, the Capilene Midweight's feature a diamond grid pattern that sheds moisture more effectively and proved even more durable than the REI Co-op Midweight in testing.
SPECIFICATIONS
Insulation Weight Class
Midweight
Material
92% recycled polyester, 8% spandex
Measured Weight(Size Small)
6.40 oz
Measured Inseam Length (Size)
Unavailable
While wearing the REI Co-Op Midweight tights during backcountry ski missions and winter trail runs, oudealbreaker couldn't help but notice that the fabric had a hard time releasing moisture (an unexpected result, since this is typically a strong suit of synthetic constructions). One tester noted, “Sweat pooled in the thicker elastic waistband, especially when I had it positioned beneath a larger backpack.” We also found thisWhen buried under our ski bibs, pairthey took longer to dry behind the knees bibs. They also lack the odor control of their Merino wool counterparts and do not feature any built-in odor control treatments to aid on this front. If smelly synthetic bottoms are a dealbreaker, Merino designs or wool blends such as the Ridge Merino Aspect High Rise Bottoms are a good choice for their naturally odor-resistant properties. Drawbacks aside, the REI Co-Op Midweight tights provide a solid performance for a modest price tag. A thinner, even more affordable version of the Midweight, the REI Co-op Lightweight Base Layer Tights, is also available.
One of our favorite midweight designs is the Minus33 Kancamagus Midweight Merino Wool Bottoms thanks to their expertly woven 235 g/sm, 100% Merino wool construction. Low-profile flatlock seams allow the bottoms to sit close to the skin without discomfort, making them perfect for cold days and nights when you're after cozy softness. Although a thicker bottom, the thermoregulation remains top notch, making them the perfect choice for an upcoming cold front with frigid forecasted temperatures. The comfortable Merino fabric is smooth, easy to layer, and doesn't grab outer layers as you throw them over top — which you will need to do.
SPECIFICATIONS
Insulation Weight Class
Midweight
Material
100% Merino wool
Measured Weight (Size Medium)
8.9 oz
Measured Inseam (Size Medium)
31.5 in
As previously discussed,, 100% Merino wool designs like the Kancamagus require thoughtful laundering and long-term care to maximize your investment. It's particularly important to lay them flat to dry rather than just throwing them into a heated cycle in your dryer. It's also important to shield them from abuse, as their delicate fibers can be easily damaged by abrasive rocks, sagebrush, or tree limbs if worn without a top shell. The Kancamagus bottoms are also super warm synthetic long underwear that may prove overkill unless dealing with specifically cold temperatures. Tester Austin Simoni mentioned, “I can't recommend these for year-round use, but if you want a reliable, inexpensive thermal layer for a day at the ski resort, this pair will do well.” Our favorite bottom is still the Smartwool Classic Thermal Merino Bottom, among the higher quality Merino wool garments. A pair of bottoms that will offer better performance appropriate to a variety of conditions is the REI Co-op Merino 185 Bottoms, which are perfect for summertime when the days are hot, but the nights get cold.
The Minus33 Kancamagus Midweight Merino Wool Bottoms offer a super soft 100% Merino wool construction that supplies ample warmth for cold alpine bivies.
The Arc'teryx Rho Bottom are a high-performing synthetic thermal underwear that offers versatility perfect for year-round use. The super lightweight design features a slim, high-waisted fit similar to a modern yoga pant. It can be worn as the foundation of your cold weather layering system or by themselves as a legging in more moderate temperatures. They are more comfortable than most synthetics, thanks to a brushed interior that resembles fleece to your skin. Another more affordable synthetic option is the Baleaf Fleece Lined Thermal. Although it lacks the wicking performance of the Rho, it features a slightly thicker construction that provides a bit more coverage, comparatively. We found the Rho easier to layer overall, and out tester points to a convenient zippered pocket on the thigh, noting “I found this really useful for holding car keys, gels, or bars during training runs and during outings on my nordic skis.”
Unfortunately, the single biggest caveat to the truly versatile and multi-sport design of the Rho Bottom comes is its expensive price tag, especially when compared to other synthetic bottoms of a similar weight. If that number proves too steep, check out the REI Co-op Midweight Tights, a more traditional synthetic bottom of a similar weight without added features. We should also mention that the Rho Bottoms feature a combination of flatlock and merrow-stitched seams (similar to welded) that can collect fuzz in high-traffic areas or when they encounter the velcro of your outer layer. That said, if you're looking for a synthetic thermal bottom that's versatile enough for year-round performance, whether worn on its own or as the foundation of your kit, the Rho is a worthy choice.
Not only did we appreciate running a dry road mid-winter, but the Arc'teryx Rho Bottoms were the perfect bottoms to get the job done. The wicking performance and brushed interior make for comfortable bottoms during uncomfortable conditions.
Credit: Trish Matheny
How We Tested
For the last several years, our men's and women's testing teams have been putting these long underwear bottoms through the wringer. Whether scaling big walls like El Capitan, traversing the vast Colorado mountain ranges in self-supported missions, backcountry skiing, or simply lounging around the cabin, our testers carefully evaluate each bottom before meticulously recording their experiences for objective side-by-side testing.
In the article below, you'll find a few key considerations of our team of experts that should help narrow down your selection.
Credit: Justin Simoni
Our process begins with researching the top layers available on the market, purchasing each base bottom individually to facilitate an unbiased assessment. We then hit the backcountry in various modes of outdoor activities, spending hours in each layer to evaluate the warmth, breathability, comfort and fit, durability, drying speed, and layering ability. We invite you to check out our assessment of women's long underwear and in-depth testing of men's thermal bottoms.
Long Underwear was tested across 6 performance metrics:
Warmth
Breathability
Comfort and Fit
Durability
Drying Speed
Layering Ability
The REI Co-op Midweight Bottoms have a similar warmth as a 200 g/sm wool bottom, while coming in just a little heavier on the scale.
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
Though the Minus33 Franconia is a midweight 100% Merino wool design, it offers a competitive drying speed, especially for a thicker long underwear bottom.
From line drying tests to measuring weight and romping in the mountains, our team of experts carefully evaluate each bottom before highlighting their strengths and weaknesses.
Why Trust GearLab
Our men's testing team is spearheaded by Justin Simoni, who is an expert on layering for cold weather. Justin is an athlete, avid adventurer, and backpacking guide based out of Boulder, Colorado. His specialties include ultra-long distance, human-powered, and self-supported adventure challenges (organized and of his own imagination) throughout various mountain ranges in the American West. These adventures require him to be exposed to the elements through many miles of ascents and descents, losing or gaining thousands of vertical feet at a time. Needless to say, this is why Justin fine-tuned his cold weather kit — so he can complete these challenges without too much discomfort. He has also worked alongside various outdoor companies over the last decade to assist with product development, sharing his years of experience from these demanding mountain adventures to improve gear.
The driving force behind our current women's lineup is Trish Matheny. After living and recreating in the Tetons and the High Sierras for the last fifteen years, Trish knows what she's looking for in high-performing long underwear. Now a current member of Yosemite's Search and Rescue Team, Trish lives outdoors most of the year, which uniquely equips her to evaluate and reconsider her layering system across all seasons. Trish is an avid rock climber, trail runner, and split-boarder when the snow arrives. Each of these passions requires different layering strategies to be as comfortable as possible in uncomfortable environments. She hopes that her experience and perspectives help you navigate the choices when selecting your next pair of thermal bottoms.
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.
No, that's not a giant croissant! Rollin up the Minus33 Kancamagus Midweight Merino Wool Bottoms really illustrates just how thick and heavyweight the 100% merino wool fabric is!
We were psyched to have the additional 5 inches of waistband that helped insulate our core during a cold day of rock climbing.
These two are no strangers to mountain pursuits, and we hope you find their experience and expertise helpful.
How to Choose a Long Underwear Bottom
Long Underwear is the foundation of a cold weather layering system. Your bottoms are meant to keep you warm by trapping body heat while also wicking moisture away from the skin, releasing that moisture through the fibers of the layer to keep you dry. Modern designs will feature body-mapping technology and ventilation panels that seek to maximize mobility and breathability for high-activity situaions. Some bottoms are versatile enough to be layered over top or worn as leggings while running or for nordic skiing. The article below seeks to identify the most important considerations when selecting a pair of long underwear.
These short pants really shine in the layering metric, we love their ability to keep bulk out of our ski boots.
Credit: Trish Matheny
Men's Long Underwear
After months of testing in the field, we record our detailed results and perspectives to share with you. The chart below highlights the scores of the best long underwear for men available today:
Women's Long Underwear
Our female testing team put a similar lineup of top long underwear for women to the test as well, taking care to track the details of their performances before identifying the best among them. The chart below displays how each pair of long undies stacks up against their competitors.
Why Does the Fabric Material Content Matter?
These days, there are tons of options between natural and synthetic fibers. Both options have their own sets of plusses and minuses. There are a few fabric combinations that dominate the market for specific preferred applications.
Be Wary of Cotton
We highly recommend shoppers avoid cotton construction in their long underwear for anything more than casual use around the home or town. Cotton is not a high-performing fabric in the face of high-output activities or inclement weather, as it will absorb both sweat and other moisture and then leave you cold, dropping your body temperature to dangerous levels if left exposed. Cotton can be perfect for sedentary cold weather activities, but should be avoided when you head out on outdoor adventures.
Fabric materials are an important consideration based on your specific objective.
Credit: Justin Simoni
Merino Wool
Merino wool is a superior fabric and the most sought after by consumers for base layer bottoms. Wool offers excellent thermoregulation, insulates even when wet, and is the softest and most comfortable next to the skin among natural fabrics. Merino can even be worn for days without holding onto body odor, so you can wear it for a long time between washes. The caveats to wool include limited durability — one hole in the delicate fabric can run like pantyhose throughout the design. This is particularly frustrating as Merino wool is often more expdealbreaker its synthetic counterparts. Wool can also stretch significantly between washes, which can make it more difficult to layer over top. Drawbacks aside, you'll have difficulty finding a synthetic bottom that performs as well in the backcountry.
The fabric of the Smartwool Classic Thermal Merino Bottom is soft and cozy, with a snug fit.
If you're looking for a midweight 100% Merino wool design that optimizes warmth and next to skin comfort, look no further than the Minus33 Franconia.
Merino wool is the superior fabric in terms of overall performance, yet it doesn't offer the same durability as its synthetic competition.
Synthetics
Synthetic long underwear bottoms are typically less expensive than Merino wool and known for their superior durability, wicking performance, and stretchy fabrics. Most of these bottoms are made of polyester or recycled polyester in addition to elastane, rayon, spandex, nylon and other materials integrated into their construction. These synthetic blends advance the longevity and overall lifetime of the final results and such materials often do a good job of wicking moisture away from the skin, releasing it through the fabric so that you remain relatively dry and warm during activity. The downside of synthetics is that they aren't as soft and comfortable next to the skin as Merino wool, and don't supply the same warmth when wet. Another dealbreaker for many people is that synthetics tend to hold onto body odor with significant use, and sometimes, no amount of tea tree oil or other antimicrobial treatment will reduce the smell.
The thick high waistband offers a fit that is similar to a modern yoga tight while the fleece-lined interior offers additional warmth and comfort.
Fit is slimmer than some other offerings, but still works for a variety of body types.
Synthetics often last longer and can more easily maintain their shape between washes due to the polyester and elastane used in their construction.
Merino-Synthetic Blends
Merino wool and synthetic fabric combinations can be said to offer the best of all worlds. These bottoms combine the naturally breathable and odor-free performance of Merino wool with the stretch and strength of synthetics such as nylon and elastane for increased durability in the final design. Most 100% Merino wool options also stretch out quite a bit between washes, so adding synthetic fibers can help such bottoms hold their shape.
The high-waisted design is flattering and allows for other layers to fasten at the natural waistline.
The Smartwool Intraknit Thermal Merino 3/4 Bottom layer well, integrating with other thick layers like a good warm wool sock.
Blended constructions combine the best of both Merino wool and synthetics, often increasing the longevity of the design, reducing the smell, and generating a soft skinside fabric face.
What Does Fabric Weight Mean to You?
Long underwear bottoms are constructed from various fabric weights ranging from ultralight to heavyweight, covering a wide range of thermoregulation needs. For most people, heavyweight or expedition bottoms are overkill. Although these bottoms offer similar wicking performance, the drying speed can be slow due to the thickness of the fabric. For those who run cold, heavy weights could be perfect for riding the chairlift during the coldest months of the year.
In contrast to heavyweight bottoms, lightweight options are typically constructed from ultra-thin materials created for high-output activities. They are perfect for backcountry skiing in the spring and are easy to layer over the rest of the season. The majority of our review features midweight bottoms due to their versatility. Midweight bottoms are often thick enough to be worn as a stand-alone legging during cooler temperatures. Still, they aren't thick enough to prevent easy layering when sub-zero temperatures hit. We recommend considering the insulation that will meet your needs before you purchase.
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.
Though the highly breathable design does sacrifice some durability, we can appreciate the sturdy waistband and flatlock seams for reinforcement in high traffic areas.
Midweight designs are typically the most versatile, although light and heavyweight options can be nice for certain activities or times of year.
What Fit and Features Do You Need?
Modern long underwear designs offer varied fits and features. Along with fabric weight, it is important to consider which are important to you. Most designs include flatlock seams to limit chafing and discomfort in high-traffic areas. They also improve the comfort of the garment next to the skin. A touch of stretch or elastane in the design is also key to allow for athletic calves, in addition to enabling free movement, especially since these bottoms are likely to be layered below ski bibs, etc.
Waistbands are also super important. Modern, high-waisted designs are typically our go-to as they are easier to layer and provide more coverage. Keep your eyes peeled for waistbands with a brushed elastic or thicker band as these are ideal to maintain comfort. And finally, what length appeals to you? You'll notice that our review often references the available cuts of each pair of bottoms. Why? Some are sold in a three-quarter length option which can be perfect for anyone who simply needs long underwear that is compatible with a ski boot. The shorter length helps to reduce bulk in the boot and prevents the bottom from being pulled down as you move. Conversely, full-length options are more versatile and provide full coverage and more warmth.
The Baleaf bottoms offer great breathability as well as multiple pockets for stashing everything from your smartphone to your nutrition that fuels your endeavors.
The waistband of the Minus33 Kancamagus Midweight Merino Wool Bottoms rides up higher than most.
Moisture wicking capabilities made the Rho one of our go-to's for shoulder season training and this stash pocket really came in handy for energy gels, bars, or a smartphone.
Although it is still rather easy to find simple, traditional long underwear designs, there are also modern designs with high-waisted fits and additional features
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How Much Should You Spend?
Unfortunately, most of the top-performing long underwear bottoms are quite expensive, requiring an upfront investment. Although synthetic base layers lack the comfort and odor-free performance of Merino wool, they are typically less costly and provide better durability. However, if you can afford to spend a little extra in exchange for superior performance, we highly recommend Merino wool. Better yet, invest in Merino wool-synthetic blends that will combine the best of all worlds and increase the lifetime of your garment.
Performance doesn't always equal price. Our testers love when affordable, budget-friendly bottoms out-perform their modest price tag.
Credit: Gus Landefeld
Conclusion
Although shopping for the perfect long underwear can be somewhat overwhelming, there are excellent choices constructed from Merino wool as well as with synthetic materials. Trying various options on will help you narrow down the broader selection and make it easier to hone in on the preferable fabric and material weight for your needs. Since these bottoms are your first line of defense against cold conditions and sit directly against your skin, it can be worth making an investment to keep you warm and safe in the outdoors. We hope our research and experience are helpful in narrowing down your selection.
Testing is a tough job but somebody has to do it. We hope you find our perspectives and experience helpful for your next long underwear purchase.
