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We took 42 base layers from Arc'teryx, Ridge Merino, Smartwool, Black Diamond, Icebreaker, Patagonia, and others to extremes during months of real-world testing to uncover the top performers for varied needs.
Base layers fabrics vary greatly in thickness, therefore, we recommend selecting the best fabric weight for your specific needs. Our testing team found that midweight options provide the widest range of performance for year round use.
There's no replacing a high-quality layering system to keep you toasty warm through the deep chill of winter. A well-designed base layer can also become a trusted companion once spring hits, offering thermoregulation when outdoor pursuits take you high and nights remain cold.
Over the last decade, our team of experts has purchased and evaluated hundreds of best-selling base layers for men and women, putting them through their paces from Yosemite Valley to the highest alpine peaks in the lower 48 and everywhere in between. All are then scored across six different performance metrics to ensure we can help you differentiate between the warmest, the most comfortable, and those that will deliver under a heavy sweat.
Here, you'll find the highest-performing options we uncovered for both genders. At the top of our list of favorites in Merino is the Smartwool Classic Thermal Merino 1/4 Zip for men, which offers a highly versatile, soft, cozy fit straight off the shelf in addition to superior warmth and breathability. For women, we similarly loved the feature-rich Black Diamond Solution 150 Merino Quarter Zip, which delivers equally on warmth and proved even more breathable, although it needs a bit of extra time to soften up with use.
Because we understand that the right layering kit will not only make or break a day in the backcountry but may also become a favorite cozy outfit for lazy days by the fireplace or for walking the dog in the early mornings, we've done the leg work to deliver you carefully curated lists of our favorite long underwear bottoms, soft fleece jackets, down jackets, and even warm socks to help keep you toasty all season long.
Smartwool has created another exceptional base layer that truly shines when the temperature drops. The Smartwool Classic Thermal Merino 1/4 Zip supplies solid warmth and ample breathability (even when wet), in addition to being noticeably versatile with a cozy fit. This Smartwool design has plenty of useful features, including a front quarter zip opening to aid in temperature regulation when you're pushing your pace, as well as a top shoulder panel with carefully placed seams meant to avoid interacting with a backpack and reduce chafe. Its 100% wool construction is some of the highest quality Merino we've tested, pairing the perfect technical performance with extremely soft, naturally moisture-wicking, and odor-free fibers. According to our tester, “The Smartwool offers just the right balance — it's a top I grab for comfort and because I know it'll do the job right.” Another great primarily Merino wool option that offers excellent odor-free performance and a pleasant softness against the skin is the Black Diamond Solution 150 Merino Half Zip Hoody.
SPECIFICATIONS
Fabric Weight Class
Midweight
Measured Weight (Size Large)
11.3 oz
Material
100% Merino wool
Fit
Semi-fitted
Measured Shirt Length (Size Large)
28.0 in
This midweight design of the Smartwool Classic Thermal Merino 1/4 Zip is tailored to cold-weather needs, so it may feel like overkill if worn in warm-to-cool temperatures. Unless you're camping under the stars in shoulder season, you may want to store this thicker layer until you're ready for ski season again. Once temperatures rise, our testers prefer the Smartwool Classic All-Season Merino 1/4 Zip, a thinner and lighter-weight option versatile enough for all seasons, just as the name implies. The majority of the fabric in both of these Smartwool designs is Merino wool, a material known for being less durable than its synthetic counterparts. If you only plan to wear your layer to the gym, out for a run, or during apres, it will hold up just fine. However, our lead tester Justin Simoni points out, “Its ultra-fine natural fibers won't stand a chance if it encounters anything abrasive, such as tree limbs or granite rock faces.” Delicate Merino such as this requires thoughtful care to preserve its lifespan, so it's important to follow the top's care instructions provided by the manufacturer. For a thermal top with a bit more grit on rugged days, the fully synthetic Patagonia Capilene Midweight Crew or the heavy Merino-synthetic blend of the Smartwool Intraknit Thermal Merino may be better, more durable choices.
Let us introduce you to your new favorite base layer that's versatile enough for year-round use: the Black Diamond Solution 150 Merino Quarter Zip. “Why did I love it so much?” says lead tester Trish Mathey. “Because it does such a great job of unifying the super soft, natural wicking performance of Merino wool with the faster drying speed and durability that polyester is known for.” This innovative layer offers Merino's odor-resistant capabilities, plus a whole lot of stretch delivered by Black Diamond's innovative Nuyarn technology, which wraps extra-fine Merino fibers around a nylon core for impressively strong results. “I encountered sharp branches on a ski tour and created a hole in the shoulder,” says Trish, “Yet amazingly it never grew any larger, even after substantial wear.” This thermal top has a slim fit and will hold its shape over time, even with continued use. It's also flattering on a variety of body shapes and sizes and proved versatile for use across multiple seasons thanks to its thin construction with an added hood, thumb loops, and 1/4 zipper that aids in trapping or offloading body heat, depending on your activity and the time of year.
We'll be the first to admit an initial skepticism when we started testing the Black Diamond Solution 150 Merino Quarter Zip. It was stiffer off the shelf than other Merino wool layers in the lineup, leaving us wanting more upfront. But, after a few washes and wears, its soft core emerged, and this layer quickly revealed itself as our first choice when headed out for a backcountry ski, a multi-pitch climb, or a trail run in the backyard. However, its lightweight construction may not be the best choice for riding the chairlift unless you layer appropriately over the top, since it's not as thick as other midweight constructions and won't stand up to such sedentary cold. On the other hand, it is perfectly built for backcountry turns. Although it's tough to match the impressive warmth of this BD Merino layer, the synthetic Arc'teryx Rho Hoody rivals it in all metrics except breathability. The Rho is also not as versatile due to its balaclava-style hood. Other options, like the Icebreaker 260 Tech Long-Sleeve Half-Zip and Smartwool Classic Thermal Merino 1/4 Zip are great for deep warmth, but the thicker hoodless constructions will limit their range of use. In contrast, the affordable Smartwool Classic All-Season Merino can be used at the base of your ski-kit or all year long due to its lightweight breathability. Just know it won't be nearly as warm.
Our testers love the Merino wool and synthetic blended fabric that provides the best of all worlds: limited odor, softness next to skin, breathability, and excellent warmth to weight ratio.
Over the years, our team has tested several iterations of the Arc'teryx Rho Hoody, which continues to sit at the top of our favorites list as a top performer for outdoor adventures. The slim fit is flattering and easy to layer, even extending a little longer over the bum to add warmth to the design. The interior is fleece-lined and offers great wicking power, though not quite as efficiently as what we've seen in other synthetic designs that incorporate a grid pattern, such as the Patagonia Capilene Thermal Weight Zip-Neck. Its material is stretchy and offers total freedom of movement, and it even comes with flatlock and merrow stitch seams to reduce chafing and irritation during activity. The result is a super soft and comfy top with great heat retention. The hood on this layer is multi-faceted. You can use it as a neck warmer, a hood, or a balaclava that equates to versatile warmth capable of adapting to your specific needs in the backcountry. Tester Trish Matheny is a big fan of the Rho Hoody, saying, “I love that it even features a small opening in the back to pull your ponytail through!” That creative design tweak helps eliminate excess bulk and draft in the hood itself. After years of testing in harsh climates, details like these keep this layer at the top of our list for synthetics, offering warmth and limited wear and tear after years of use and abuse.
SPECIFICATIONS
Fabric Weight Class
Lightweight
Measured Weight (Size Small)
7.6 oz (size medium)
Material
Torrent 190 stretch fleece with Polygiene: 84% polyester/16% elastane
Fit
Slim fit
Torso Length
Medium
Even though the Rho Hoody is treated with a polygiene odor treatment, it still retains body odor, a classic drawback for synthetic designs. The layer also isn't as breathable as other synthetics we tested, as there is a lot of fabric around the neck, and the design doesn't feature a zipper to offload some of that body heat. For this reason, we love this layer as a stand-alone piece during the change of season, but may choose something like the Patagonia Capilene Thermal Weight Zip-Neck for high-activity days mid-winter. “Think of the Rho for crisp days in the spring and fall, or even summer mornings before the heat of the day arrives,” says Trish. If breathability is key and you don't have an allergy keeping you from wool, check out the Black Diamond Solution 150 Merino Quarter Zip. This layer isn't as thick as the Rho but has a hood, a quarter zip, and thumb loops for versatile warmth. It is also worth mentioning that the Rho Hoody isn't as affordable as other synthetics we tested. However, it is one of the most durable base layers in the lot and can withstand years of use in the backcountry. If you're into synthetics and don't need a layer for every day, check out the more affordable yet feature-heavy REI Co-op Midweight Base Layer Crew.
The REI Co-op Midweight Half-Zip is an excellent choice for those on the hunt for an affordable base layer that won't break the bank. The 220 g/sm midweight construction features a soft, stretchy fabric that is thick enough to provide a barrier to the elements without a rigid synthetic feel against the skin. During our extensive testing period, our testers couldn't help but appreciate the warmth and breathability of the midweight construction. Justin Simoni, our lead tester, noted: “Although more affordable than most, this layer includes key features that I find make it versatile for regular use throughout the year — a win-win on all counts!” Such features include thumb loops and a half zipper at the neck to either help you bundle up and trap body heat when cold or to open up and increase breathability once temps or activity pick up. In addition to the soft and flexible fabric, its thoughtful construction also features flatlock seams to prevent discomfort and chafing, especially at the shoulders if one wears a backpack over top.
SPECIFICATIONS
Fabric Weight Class
Midweight
Measured Weight (Size Large)
10.0 oz
Material
92% recycled polyester, 8% spandex
Fit
Semi-fitted
Measured Shirt Length (Size Large)
29.0 in
Although not a top performer in any one test metric, the REI Co-op Midweight Half-Zip puts up above-average scores across the board. We have had the pleasure of testing softer, warmer, and more feature-rich thermal tops. However, the Midweight stands out among those layers with its more affordable price. If you're interested in Merino options that can rival the REI Midweight's affordable performance, check out the Icebreaker Merino 200 Oasis Half Zip. It has a softer next-to-skin feel if you can accept that it won't be able to keep up with the REI Midweight's overall durability for everyday use. If you're just looking for a simple base layer for everyday use rather than a high-performing technical layer to deliver on outdoor escapes, check out the Carhartt Base Force Midweight Crew. If your activities will keep you close to home and you are shopping on a budget, this is a nice choice that skips the bells and whistles to offer low-cost comfort instead.
Small details such as discreet thumb loops featured in the REI Co-op Midweight Half-Zip design help to keep your hands covered and warm, while aiding in easy layering over top.
The REI Co-op Midweight Base Layer Crew is the perfect option for those seeking a synthetic base layer crew that combines solid performance with a smaller price tag. We love synthetic layers available for a lower price than the Merino wool competition and don't skimp on overall performance. The midweight construction features a soft and stretchy fabric with a flattering fit that rests close to the body but isn't too tight to wear on its own during crisp days in spring and fall. While not as high-performing as the Arc'teryx Rho Hoody or Patagonia Capilene Thermal Weight Zip-Neck, the Midweight isn't completely stripped down and basic. For instance, its synthetic construction is highly durable. One tester pushed its limits on an extended trip to Indian Creek, saying, “The climbing here is physical and the routes are long and demanding, yet this layer held its own, and I especially liked the flatlock seams — they preventing discomfort even when I was contorted into awkward positions to reach the anchors.”
SPECIFICATIONS
Fabric Weight Class
Midweight
Measured Weight (Size Small)
7.4 oz
Material
92% recycled polyester, 8% spandex
Fit
Regular fit
Torso Length
Medium
The REI Co-op Midweight Base Layer Crew is made of a polyester blend, which unfortunately, almost immediately started to smell after use. Perhaps it's worth mentioning that this is true of most synthetics we've tested over the years and not unique to this garment alone. Adding a little tea tree oil during the wash cycle isn't a bad idea to cut the stench. If naturally odor-resistant options sound more appealing, Merino wool layers like the Black Diamond Solution 150 Merino Quarter Zip or Ridge Merino Convict are good options. Although each is built of a Merino wool-synthetic blend fabric, neither held onto unwanted odors during testing. One other drawback to the REI Midweight is its long drying speed and less efficient breathability. Both are due to its thicker construction and tightly woven polyester. For this reason, we recommend the Midweight for low-output missions versus adventures that will produce excess sweat. Any layer can cool you down if it's trapping some of that moisture you create, and this one proved it's slow to release and dry. That said, its flattering fit and durable construction are tough to beat, especially considering the affordable price.
While Merino wool ultimately takes the cake when it comes to superior performance, its typically expensive price tag can often be a barrier to entry for some shoppers. If you're interested in a base layer constructed of 100% Merino wool far exceeding its modest price tag, we highly recommend the Merino.tech Crew. This lightweight crew features ultra-fine micro-fibers that provide a soft interface with the skin without the infamous “itch” often associated with less refined wool. This crew fits close to the skin, making it easy to layer beneath mid and outer layers during cold winter activities or when worn alone inside a sleeping bag during a cold bivy. “A lighter fabric weight like the Merino.tech Crew is usually what I prefer on my chillier runs since I tend to build up a lot of heat,” notes Justin Simoni, our lead reviewer.
SPECIFICATIONS
Fabric Weight Class
Lightweight
Measured Weight (Size Large)
6.8 oz
Material
100% Merino wool
Fit
Semi-fitted
Measured Shirt Length (Size Large)
29.0 in
While you certainly can't beat the price, there are a few flaws we should call out in the Merino.tech Crew's design. Its 100% Merino wool construction simply won't be as durable as what is offered by its synthetic counterparts, as it is not blended with any other material to strengthen the ultra-fine wool fibers against inevitable abrasions. Layers made of blended wool, such as the Smartwool Intraknit Thermal Merino, provide reinforcement to the delicate fibers that the Merino.tech lacks. For the same reasons, following the specific care instructions for such a delicate crew will also be necessary, at least if you want to maximize your investment. The slim fit also isn't for everyone and could limit mobility for some. It also utilizes overlock seams rather than flatlock seams, which could create discomfort for those with especially sensitive skin. Other affordable but more spacious options include the Meriwool Merino 250 Long Sleeve. It is quite a bit thicker and much warmer than the Merino.tech crew, and it has flatlock seams. That makes it of higher construction quality and less susceptible to durability issues.
Excellent slim fit is flattering and easy to layer
Thoughtfully placed seams for noticeable comfort
Super thin and breathable
Quick drying
REASONS TO AVOID
Fabric is susceptible to durability issues
Lacks stand-alone warmth for year-round use
The Smartwool Classic All-Season Merino is an incredibly lightweight, thin, primarily Merino wool base layer that remains affordable without skimping on performance. A combined 88% Merino wool and 12% nylon construction means it has the best of both worlds: Merino wool's naturally odor-free wicking performance with the added durability of core-spun nylon to help the layer hold its shape. This is one of the lightest base layers we've tested, and that makes it the perfect base for your cold-weather kit, thanks to its slim fit that is easy to build over. “I found this perfect for wearing under a ski bib during laps at my favorite ski resort,” says one tester. Our test team also sang its praises when worn on its own for hiking or trail running during the spring and fall when mornings are cool. Even after multiple uses between washes, this layer never picked up any noticeable smells, and the raglan sleeve design proved comfortable when worn with a pack. Merrow stitching and flatlock seams eliminated worries about chafing, while the longer fit provided more coverage.
SPECIFICATIONS
Fabric Weight Class
Lightweight
Measured Weight (Size Small)
4.5 oz
Material
Merino jersey: 88% Merino wool, 12% nylon core
Fit
Regular fit
Torso Length
Medium
The moisture-wicking performance of the Smartwool Classic All-Season Merino top is tough to beat. Our testers recommend it for those seeking a highly breathable, quick-drying base layer that has a slim fit and is easy to layer over the top of. While more affordable than most, it isn't the most inexpensive Merino wool option out there. For those seeking an even less costly 100% Merino wool crew with a thicker (and warmer) construction at a surprisingly low price, check out the Merino.tech Merino Crew. Although this layer won't provide enough durability for everyday use, it's a perfect choice for those cold-weather vacations where you plan to ride the chairlift and then bury it at the base of your cold-weather kit for the rest of the year. For those of you who plan on earning your turns or training during the cold months, you won't be disappointed in the layering ability, breathability, and wicking performance of the All-Season. And if you're not interested in investing in a Merino wool construction, the REI Co-op Midweight Base Layer Crew is our favorite affordable synthetic crew.
The Classic All-Season is a Merino wool blended design that performs well at the base of other layers or as a stand alone piece during the warmer months of the year.
Of all the base layers we've tested throughout the years, the Black Diamond Solution 150 Merino Half Zip Hoody is the one we find ourselves reaching for the most. The 150 g/sm Merino wool blend features a helmet-compatible hood, a quarter zip, and thumb loops — it strikes the perfect balance between light and midweight performance. The longer sleeves and torso, paired with handy thumb loops, help you cover up and stay warm, or you can open up the quarter zip to increase breathability and offload some body heat. The design features an athletic fit that hugs your body shape to efficiently wick moisture away from the skin before releasing it through the breathable wool-blend fabric construction. This layer is perfect as a first layer or when worn on its own as temperatures rise.
SPECIFICATIONS
Fabric Weight Class
Lightweight
Measured Weight (Size Large)
8.0 oz
Material
Nuyarn: 78% Merino wool, 22% polyester
Fit
Slim fit
Measured Shirt Length (Size Large)
29.0 in
Unfortunately, the Solution Hoody's trim fit isn't likely to be flattering on all body types. Our testers found it too tight for some body types to wear comfortably, with one commenting, “It was not comfortable for me to move as needed - I found it too tight around the shoulders and in the armpits.” While Black Diamond's NuYarn wool blend is more durable than most, this fabric is thin and stretchy. This means it won't last as long as a fully synthetic layer. If you'd rather invest in a more durable Merino wool layer, the Ridge Merino Aspect Midweight is a great layer to check out. It features a similar fabric weight, a blended construction, and a hood for greater versatility. Unlike the Aspect, the Solution is one of the most expensive Merino wool blends we've tested. So be sure you need all the added performance features before you invest. That being said, if you aren't discouraged by the price tag or the fit, the Solution will definitely become your go-to layer for nearly any outdoor activity you choose.
The Icebreaker Merino 200 Oasis Crewe is a 100% Merino wool design with a super-soft construction and flattering fit. Our testers couldn't help but notice thoughtful features that include flatlock seams in specific locations to increase comfort and durability, as well as gusseted underarms that allow the layer to move with you, never limiting your full range of motion. Tightly-woven and ultrafine 18.9-micron fibers combine with a slim fit to aid in this layer's ability to trap body heat while also moving sweat away from the skin. You'll find a slightly more affordable version of this layer in the Smartwool Classic All-Season Merino. Just be aware that the fabric is much thinner and not nearly as soft, although you can get use out of it all year long.
SPECIFICATIONS
Fabric Weight Class
Lightweight
Measured Weight (Size Small)
6.3 oz
Material
100% Merino wool
Fit
Slim fit
Torso Length
Medium
Unfortunately, the lightweight construction of the Oasis Crewe doesn't offer a high degree of breathability once layered beneath outer layers within a cold weather kit. While it had no trouble wicking moisture when exposed to open air, the moisture sat absorbed far longer once more layers were added. This longer drying speed is palpable when out for a day of backcountry touring. One tester points out, “I'm often sweating on climbs and cooling off during the descents, so the cold of that moisture was noticeable on the way down.” We discovered its slower drying speed during our line dry tests and noticed that a few other Merino options fared better. The Patagonia Capilene Thermal Weight Zip-Neck or Ridge Merino Convict are options that deliver better breathability, dry time, and durability. But the Oasis still stood apart from many other crews we've tested over the years due to its soft and cozy wool construction, slim and flattering fit, and durable flatlock seams placed in locations to increase comfort and lifetime performance.
The Smartwool Intraknit Thermal Merino features a uniquely creative seamless Intraknit technology and strategic paneling to prioritize breathability and durability. This 50/50 Merino wool-synthetic blend also aims to reduce overall bulk, featuring a slim and athletic fit that sits close to the skin without limiting your ability to move. For this reason, the Intraknit is also easy to layer over when preparing for the coldest winter conditions. The design includes extra length in the sleeves and torso for added coverage and a drop-tail hem to keep your backside covered no matter how you plan to move. The midweight construction is thicker than most crews we tested, making it perfect to wear on its own during the change of season.
SPECIFICATIONS
Fabric Weight Class
Midweight
Measured Weight (Size Large)
8.0 oz
Material
53% Merino wool, 45% polyester, 2% elastane
Fit
Slim fit
Measured Shirt Length (Size Large)
29.0 in
All positive attributes aside, the Intraknit Thermal has flaws and weaknesses within the innovative design. The Merino wool blend is subject to pilling, especially in high-traffic areas like under the arms and where it interacts with a pack. The slim and athletic profile can also be problematic for some body types, as it can be uncomfortably tight in the arms and shoulders for some athletes. In this case, we recommend layers like the Patagonia Capilene Cool Lightweight L/S that offer a more forgiving fit. With all the creative technology included in the Intraknit, we were surprised to find some seams placed in locations that cause noticeable discomfort, such as beneath a backpack strap where it rubs and eventually causes chafing. Flaws aside, we can appreciate the unique construction that supplies excellent thermoregulation when exposed to the elements for an extended period.
Micro-grid fleece interior is soft against the skin
REASONS TO AVOID
Fabric holds body odor with use
Not a traditional thermal weight
Thumb loops need improvement
The Patagonia Capilene Thermal Weight Zip-Neck offers a unique spin on what you'd expect from a traditional base layer top. The micro-grid fleece patterning and lofted design allow the layer to maximize airflow while simultaneously trapping body heat generated during activity. As long as you're on the go, it is the perfect stand-alone piece for the change of season. Whether trail running, rock climbing, or mountain biking, this layer efficiently sheds moisture faster than most. Our tester reports, “Although I disagree with the advertised thermal weight on this top, its polyester blend is designed to move with you, and I like that.” Offset shoulder seams combine with a touch of stretch in the material to allow for a full range of motion while prioritizing exceptional breathability and softness next to the skin.
SPECIFICATIONS
Fabric Weight Class
Midweight
Measured Weight (Size Small)
4.8 oz
Material
Polartec Power Grid with HeiQ Pure: 92% recycled polyester, 8% spandex jersey
Fit
Regular fit
Torso Length
Medium
Although equipped with a polygiene odor control treatment, we couldn't help but notice the Capilene Thermal retaining body odor almost immediately. Our lead tester selected this versatile layer for a fall ascent of El Capitan, yet couldn't wait to get it off due to the smell retained over just those three days. If odor retention is a dealbreaker for you, let us suggest a Merino wool-blend layer of similar design: the Ridge Merino Convict - Women's. While the minimal thumb loops on the Capilene Thermal make it easy to layer, the thin elastic bands that serve as those loops cause discomfort, and the results still don't provide full coverage over the hand when the temperatures drop. Caveats aside, this layer stands out as a unique design that prioritizes the warmth and comfort of Polartec in addition to a lofted micro-grid pattern that maximizes breathability. If you're interested in a synthetic layer that provides more stand-alone warmth, the Arc'teryx Rho Hoody has a balaclava-style hood and brushed-fleece interior for superior comfort and should not be missed.
Although the trail was thick with tourists, we loved how the Patagonia Thermal Weight performed on a spring run in Yosemite Valley. The breathability of this design is tough to beat.
Credit: Trish Matheny
How We Tested
GearLab's testing teams have thoughtfully selected and purchased hundreds of men's and women's base layers over the last 10 years. Our expert team really puts these layers to the test, whether pursuing various outdoor objectives or simply lounging around at the house to better determine overall comfort and fit.
GearLab is always on the lookout for the latest and greatest base layers available on the market. We spend many hours researching and carefully selecting the layers we think will likely deliver the most noteworthy performances, never accepting any products for free to ensure we remain unbiased during side-by-side testing. Our testers then spend many hours out in the field and the “lab,” meticulously recording data to capture objective assessments and subjective insights across all key metrics for each base layer. Those results are then distilled into a highlight reel so we can present the top performers to you here. We tested highly popular base layers for women and examined the top-selling thermal tops for men, including soft Merino wool options to technical synthetic blends, before honing in on a handful of favorites that stand out above the rest.
Base Layers were tested across 6 performance metrics:
Warmth
Breathability
Comfort and Fit
Durability
Drying Speed
Layering Ability
Although 100% Merino is valued for its incredibly lightweight warmth and breathability, those features can be augmented and amplified when blended with synthetic materials.
Testing in the "lab" can mean many things, and with base layers, it includes soaking each top and tracking its dry time.
We love a good layer that is warm enough to wear alone on an early spring run, like the Icebreaker Merino 200 Oasis.
We measured everything from overall warmth and breathability to drying speed to carefully evaluate the individual performance of each layer.
Why Trust GearLab
Our GearLab testing team consists of outdoor enthusiasts from various backgrounds and geographical locations who know a high-performing base layer when they see one or when they wear one. To appropriately evaluate each base layer's performance, we have divided our testing team into separate teams for each gender.
The lead reviewer for our Men's Base Layer lineup is Justin Simoni. A local of Colorado, Justin maintains his fitness by performing year-round ascents of Longs Peak, often relying on human-powered bike-from-town approaches. For the last ten years, he poured his energy into long-distance bikepacking races and pursuing mountain FKTs (Fastest Known Times), including the Tour Divide, Colorado Trail Race, and even his own personal 14er challenges. If he understands anything, base layers are critical to moving comfortably through remote locations, especially when awaiting the heat of the rising sun.
Leading our Women's testing team is Trish Matheny. After spending a decade living and exploring the Teton Mountain Range, she knows exactly what to look for in a good base layer. Whether prioritizing backcountry miles on her splitboard, trail running throughout the Greater Yellowstone backcountry, climbing multi-pitch routes high in the alpine, or simply trying to stay warm in camp, Trish has in-depth experience selecting the best layer for her chosen activity. After relocating to California and becoming a member of Yosemite's Search and Rescue Team, Trish now spends most of her time living outdoors, utilizing her skills and experience to provide thoughtful information that will hopefully help you select the best base layer to meet your specific needs.
For a mostly Merino wool layer, The Solution dries pretty quickly, and it breathes like a dream.
Another example of a layering system: we used the REI Co-op Midweight Half-Zip as our base layer, with a gridded fleece mid layer over that, and a down puffy jacket over everything.
The Solution Hoody features a tight, athletic, next to skin fit.
Trish and Justin put these layers to the test, whether training indoors or playing in the mountains. They hope their hard-earned expertise will help you with your next purchase.
How to Choose a Base Layer
Base layers are a key component to any cold-weather kit, but selecting one is no easy task. These layers must be capable of wicking sweat and moisture away from the body while maintaining body heat and providing a cozy next-to-skin feel. Many modern designs even feature gussets in specific locations to maximize mobility during various outdoor activities. Some layers are perfect for layering over the top of, while others provide enough stand-alone performance to be worn independently. Below are a few key considerations that will help you select the best base layer for your specific cold-weather pursuit.
Our testers love the slim fit and ultra fine Merino wool that increased comfort next to skin without sacrificing durability on the Ridge Merino Aspect.
Credit: Lindsey Fell
Men's Base Layers
We conduct extensive testing with in-depth notes to reveal the best base layers for men. The chart below summarizes the performance results of each layer we reviewed on our hunt for the best men's thermal layers available today.
Women's Base Layers
GearLab's expert female testing team pulled out all the stops while examining the top base layers for women, putting each garment through diverse tests to evaluate overall and comparative performances, as shown in the chart below.
Why Choose Natural Versus Synthetic Fibers?
These days, base layers are typically constructed from natural fibers such as Merino wool, bamboo, Tencel, and hemp, or a variety of synthetics such as nylon, spandex, polyester, etc., or a combination of the two. Merino wool is deservedly the most sought-after fabric for base layers due to its ability to maintain warmth even when wet and its naturally wicking antimicrobial fibers that help move sweat and resist odor. Perhaps most importantly, it can also be remarkably soft against the skin. Yet, these superpowers do not come without a few trade-offs. Namely, reduced durability due to the delicate natures of the fibers, a slow drying speed, and, most notably, steep price tags. That being said, Merino is a superior fabric that is tough to beat.
This quickly became one of our favorite crew base layers thanks to a thoughtful design and super soft 100% Merino wool.
The front 1/4 zip on the Smartwool Classic Thermal Merino helps with dumping excess heat quickly, coming in handy when you're layered up and conditions change quickly.
Although more expensive and less durable, Merino wool offers naturally odor-free wicking performance and next-to-skin comfort.
By comparison, synthetics are known for their lasting durability. Recycled polyester, torrent, nylon, spandex, and elastane combine to offer superior stretch, form, and enhanced mobility. They also often allow for a more breathable, faster-drying design, be it on the body or the line. The major drawback most people associate with synthetics is their tendency to hold onto body odor- Capilene, anyone? That being said, these fabrics are often more affordable and last longer than their Merino wool counterparts.
Synthetics are often much less expensive than Merino or higher-end wool blends and may prove far more durable, even if they may not always perform quite as well in other metrics.
The REI Co-op Midweight Half-Zip didn't at first grab our attention, but we found a high performance base layer, once we started running our lab tests and taking it out onto the trails.
Synthetics are known for a less expensive price tag and a highly durable construction, even if they may also hold onto body odor after extensive use.
Are you looking for the best of both worlds? Consider a Merino wool-synthetic blend. This hybrid weaves the warmth and softness of Merino wool with stronger synthetic fibers that help to increase the garment's overall durability and ability to maintain its shape between washes.
Though pockets can add a little bulk, they can be great for stashing a car key, an essential gel, or a credit card for safe keeping during your workout.
Merino offers extraordinary warmth and odor control, and tops woven of this high-quality natural fiber can be designed to deliver equally impressive breathability and comfort.
Merino wool and synthetic blends combine the best of all worlds, offering high performance without losing shape or holding onto body odor after multiple uses between washes.
What Is The Difference Between Fabric Weights?
While fabric weights range from ultralight to expedition weight, our review focuses specifically on lightweight, midweight, and heavyweight fabric options. As one might guess, lightweight base layers can be the perfect choice for warm weather conditions. Think of sleeping in the desert during the summer heat when layering is minimal, besides nights spent under the stars when colder temperatures settle. When placed against the skin as the base of your cold-weather kit, lightweight layers can also be a great choice for high-output activities during the coldest months of the year. Midweight constructions are perhaps the most versatile options out there, which explains why they tend to dominate both the men's and women's reviews. These are perfect stand-alone layers for the spring and fall but still work well at the base of your kit for resort and backcountry turns in the winter. Heavyweight layers are for those seeking a high degree of warmth above all else. These thicker tops can be difficult to layer and less versatile across seasons and activities. However, if expedition skiing or exploration features into your calendar during the coldest months of the year, it may warrant a thicker choice.
An example of a layering system. Base layer, fleece mid layer, soft shell, and down puffy. The Patagonia Capilene Air, pictured here, traps heat extremely well in a layering system but as a stand-alone layer, air cuts right thru it.
For a small investment, layers like the Arc'teryx Rho Hoody will offer versatile performance for many adventures to come.
We tested every option from lightweight to heavyweight and found that midweight designs offer the most versatility.
What Specific Fit And Features Are Important to You?
We recommend trying on your next base layer before you purchase to select a top that fits well and sits next to your skin without limiting your range of motion. This helps to prevent cold drafts and allows the thermal layer to wick moisture effectively. Pay attention to manufacturer product details on such things as fit — regular, trim, or slim — to determine the cut of the layer.
The Smartwool Intraknit has a slim, long fit, and is slightly longer in the back.
We appreciate the stretch fabric on the synthetic Cotopaxi Liso, which provides great range of movement.
Base layers are available in a variety of different cuts; while some may feel too restrictive, oversized layers don't provide the best performance.
Base layers come with all sorts of bells and whistles these days. There are many feature options, from hoods to thumb loops to longer cuts, zippers, and more, and each serves a different purpose. While our lead women's tester prefers a Merino wool blend with a 1/4 zip, hood, and thumb loops, this could be overkill if you are shopping only for an annual resort skiing trip. While things like hoods, extra zippers, lofted fabrics, and thumb loops can provide additional warmth for those on the go, they also take up more space in your cold-weather kit. Ultimately, these features are a personal choice, so we recommend identifying the specific uses you'll have for your layer before you make your investment.
A great base layer can be very simple in design, or it can come with all the bells and whistles -- hood, pockets, thumb loops, and more. What matters most is that it has the features you require to make the most of your day outdoors.
The Arc'teryx Rho LT Crew has a handy zippered pocket on the front to stash small items like keys, a credit card, or even a smaller-sized phone.
Some base layer designs are feature-rich, including versatile hoods, zippered pockets, and more.
How Much Do You Need to Spend?
Speaking of investments, how much should you spend on your next base layer anyway? While this answer will vary among consumers, we can point out that top-of-the-line Merino wool layers will often cost a pretty penny and boast more features using high-performing materials. Synthetic designs will often be more affordable, with the most affordable options often sacrificing key features that enhance comfort next to skin, mobility, and odor resistance. Some synthetic options in our review also feature lofted patterning to enhance breathability and capture body heat generated during high-output activities. Great Merino wool base layers are also available at a fraction of the price of their top-performing counterparts. Unless you plan to wear your layer day in and day out (JMT, PCT, anyone?), you can often get away with a lower-cost option providing enough thermoregulation for most outdoor activities.
When hitting the slopes or climbing in the fall, this layer is perfect for those who prioritize both quality and performance.
We love the Black Diamond Solution 150 Hoody for backpacking in cold conditions.
Some athletes and backcountry enthusiasts require the highest-performing base layers with the most modern and innovative technologies, but most consumers will find that a more affordable option easily meets their needs.
Conclusion
Although there are a ton of options out there, we hope this article will help you select the best layer for your specific needs and body shape. After months of research, product selection, in-field testing, and sharing our experiences, we aim to provide specific details about the attributes of each layer to inform your heading into the next purchase better. We hope you have as much fun in these layers as we did.
We sure had fun testing these layers and hope our insights and experiences help inform your upcoming purchase.
