Best Long Underwear for Men of 2024
COMFORTABLE, MOISTURE-WICKING, AND INSULATING BASE LAYERS FOR MEN
Home > Gear Reviews > Apparel
April 1, 2024
When I was a kid, long underwear meant waffle-textured cotton long johns. These inevitably got soaked, soggy, and loose, with the crotch inevitably hanging down by the knees because the waterproof, insulated pants we wore over them didn’t breathe. We essentially steamed in our own sweat. Or, as our jeans absorbed water on a leg cuff, the long johns acted as a wick and soaked through, leaving our legs cold, wet, and goose pimpled. Within a season the long johns were positively warped out of shape with an elastic waistband that looked like the scalloped edge of a clam shell. It was better to just go without them, even though the folks scolded us for that.
Thankfully that’s not the case with modern long undies, better known these days in the outdoor world as base layer bottoms. The best are great at insulating your gams while remaining in shape and moving any perspiration from your skin outward, keeping you warm, comfy, dry, and hopefully not that stinky between washes, while lasting for years with a little care.
Some of the most popular and best-loved men’s and women’s underwear these days aren’t looking to space-age, insulative materials, like some of our favorite pieces of outerwear and mid layers, but rather good ole’ fashioned wool (merino wool, that is).
Long underwear is definitely a category where the consumer wins, with plenty of great choices out there from leading competitors at what’s usually a pretty competitive price point. Our least expensive winners will run about $60 and even our overall favorite is relatively affordable at around $100. Having worn some of the same pairs of long johns for four or more years while ice climbing, mountaineering, pedicabbing and skiing in the front and backcountry, we definitely think we’ve extracted that value out of them.
Looking for long-sleeve base layer shirts? See our guide to Best Base Layer Tops.
We create reader-supported, objective gear reviews independently selected by our editors. This story may contain affiliate links, which help fund our website. When you click on the links to purchase gear, we may get a commission – without costing you an extra cent. Thank you for supporting our work and mission of outdoor coverage for every body! Learn more.
Men’s long underwear comparison table
| MEN'S BASE LAYER BOTTOMS | TREELINE AWARD | MATERIAL | SIZES | WEIGHT | FLY |
|---|---|---|---|---|---|
| Icebreaker 200 Oasis | Best Overall Read review |
Merino Wool | S-XXL | 178 g | Yes |
| Icebreaker 260 ZoneKnit Merino Thermal Leggings | Best Upgrade Read review |
100% Merino Wool | S-XL | 192 g | No |
| Patagonia Capilene | Best Synthetic Read review |
100% recycled polyester | XS-XXL | 170 g | Yes |
| Rab Syncrino Leggings | Best lightweight Read review |
53% Polyester (32% recycled), 47% Merino Wool | S-XXL | 122 g | No |
| Ibex Woolies 2 | Best heavyweight Read review |
Merino | S-XXL | 208 g | Yes |
| Artilect Flatiron 185 | Best technical Read review |
91% Superfine Nuyarn merino wool, 9% Nylon | XS-XXL | 174 g | No |
The winners
Best overall long underwear: Icebreaker 200 Oasis
Material: Merino Wool
Available sizes: S-XXL (full-length and 3/4 length available)
Weight: 178 g (men’s medium as tested)
Fly: Yes
What we liked: Comfort, good waist band, good leg cuffs
What we didn’t like: Price, not as suitable for more variable weather conditions as some other options
If you’re looking for one pair of base layer bottoms for just about everything, you can’t go wrong with the Icebreaker 200 Oasis. Too often, we find that slogans are just that, slogans. In this case, however, when Icebreaker says “World’s Best Base Layer,” they can get away with it. Icebreaker’s merino is exceptionally comfortable, thanks to using fine wool fibers of 17 microns. In some cases, like its MerinoFine wool, Icebreaker’s fibers are only 15.5 microns thick. We’ve had various Icebreaker tops and bottoms for years and they’ve held up considerably well for a merino base layer. Thus far, these are no different.
We’ve worn these on days on the lift at Loveland Ski Area, where temperatures stayed below 20 with nothing but a shell over them, and were fine. We’ve also taken them into the backcountry to alpine tour Hidden Knoll at Berthoud Pass and didn’t sweat out on a day when temperatures were around freezing.
These have everything we want in a good base layer bottom, including a comfortable waistband that doesn’t sink down or ride up the waist, even after being worn all day or multiple days in a row, nor did we notice any significant sagging in the crotch after wearing them for multiple days between washings. Similarly, the ankle cuffs don’t ride up—there’s no tech stuff there, they just worked well. They were also comfortable under ski and mountaineering socks in the winter. We also love the natural anti-stink properties of merino wool and, as most merino pieces do, these never retained odor as too many synthetic options do.
ICEBREAKER 200 OASIS
The 200-gsm-weight fabric is heavy enough for most conditions where you’ll need a base layer bottom, but not so heavy and warm we got too hot on some days. We didn’t get too sweaty in them on warmer days in early December doing high-output activities like alpine touring and snowshoeing, and were warm for most days at the slopes in just a good shell, like one of our favorites, the Outdoor Research Hemisphere II bibs.
Others agree. The Icebreaker 200 Oasis has racked up over 225 positive reviews at REI with an average of 4.9 out of five stars. One reviewer noted their durability: “The last one I bought was in 2012 and it endured a ton of trail running. I finally had to replace it with this one and no doubt it will keep me warm on my trails until 2032.” Another noted: “I live in Minneapolis where it's necessary to wear long underwear for 6 out of 12 months. These are just the right weight to keep me warm outdoors, but not too warm indoors.”
Best upgrade long underwear: Icebreaker 260 ZoneKnit Merino Thermal Leggings
Material: 100% Merino Wool
Available sizes: S-XL (full-length and 3/4 length available)
Weight: 192 g (men’s medium as tested)
Fly: No
What we liked: Body-mapped ZoneKnit technology allows these thermal leggings more versatility than most other leggings
What we didn’t like: Very expensive, no fly
The Icebreaker 260 ZoneKnit are some of the most versatile leggings we tested. While they’re considered a 260-weight piece, they also have Icebreaker’s thinner, ZoneKnit mesh panels, that allow for more perspiration to pass through areas that are more prone to sweating, like at the lower back and behind the knees.
That gave us a base layer bottom we were happy to wear on a recent day at Jones Pass where we were riding snowmobiles in the backcountry and alpine touring. While the temperature rose above freezing—it was warm enough that sunny, powdery snow clumped to our skis (yes, time for more wax!)—but even when skinning up we didn’t sweat out. Nor did we get cold when waiting for the snowmobiles in the much colder glade shaded areas. As such, they’ve been one of our favorite go-to base layer bottoms this whole testing season—even though we have the older orange version.
ICEBREAKER 260 ZONEKNIT MERINO THERMAL LEGGINGS
They did have some drawbacks, though. Chiefly, price. While our favorite overall, the Icebreaker 200 Oasis, costs a reasonable $95, these retail for $165 (you can usually find them for less), and they don’t even have a fly! Still, they were comfortable and we didn’t experience any sagging over multiple wears between washes.
The ZoneKnit technology is awesome, and Icebreaker won an ISPO Sustainability Award for its use of the material in its Icebreaker ZoneKnit Hoodie. But at over $150 the price isn’t sustainable if you need to buy more than one pair over a decade. We haven’t had our pair that long but, like our experience with other Icebreaker pieces, hope it’s durable enough to last for a long time.
We haven’t found many professional reviews of these particular long johns, but all nine customer reviews on backcountry.com give them five stars. The women’s version is also highly rated. It was Outdoor Gear Lab’s highest ranked choice, gaining it an Editors’ Choice Award there. Outdoor Gear Lab noted: “If you want to invest in a high-performance pair of long underwear bottoms that deliver warmth and breathability, look no further than the 260 ZoneKnit. These 100% Merino bottoms offer enough ventilation and wicking capabilities for the most demanding winter sports.” They didn’t test the men’s version, but our own testing of the men's model agrees."
Best synthetic long underwear: Patagonia Capilene Midweight Base Layer Bottoms
Material: 100% recycled polyester
Available sizes: XS-XXL
Weight: 170 g (men’s medium as tested)
Fly: Yes
What we liked: bluesign-approved recycled polyester, a good, cheaper alternative to merino wool, durable fabric
What we didn’t like: Looser fit, not as soft as some merino options, not as good at at odor prevention
People have sworn by the Patagonia Capilene base layers for years, if not decades, at this point. The company has continually updated this popular, synthetic base layer fabric over the years as well. It’s now made from entirely recycled polyester and has an odor-resistant treatment from HeiQ.
We wore this thin base layer on early-season backcountry days at Berthoud Pass when we were getting used to our skis again for the season. We found the diamond-grid pattern in the Capilene fabric did a good job of insulating while providing excellent wicking properties and didn’t experience any wetting out. We didn’t test them in extremely cold situations as they’re made of a fabric that was among the thinnest we tested.
PATAGONIA CAPILENE
Though we don’t usually run in base layer bottoms, opting for running pants or tights instead, we do think the Patagonia Capilene Midweight Base Layer Bottoms would work fine under a pair of shorts and wouldn’t be as worried about bashing it against rocks and hard surfaces on a trail run or hike as we would be with a wool base layer.
Still, we didn’t like the fit or fabric feel on these as well as the best wool base layers we tested. The fabric was looser around our thighs, crotch, knees and calves and the ankles as well, making them feel bulkier than the against the skin fit of base layer bottoms like the Artilect Flatiron 185 Leggings, for instance. We also noticed Patagonia’s Capilene fabric just didn’t feel as soft as the wool in our favorite base layer bottoms, the Icebreaker Oasis. We did notice they had more scent retention than wool base layers as well, which is what we'd expect of a synthetic base layer.
This is a very good pair of long johns and one we look forward to doing more testing in. They’re particularly great for the price. Our favorite Icebreaker Oasis leggings retail at $105, the Patagonia Capilene leggings run $80.
Despite the somewhat baggier fit, which others have noted, they’re highly regarded earning over 45 reviews with an average of 4.6 stars at REI. One reviewer noted: “I won’t ski with anything else… I can’t put in words how much I love the Capilene base layers. They are warm, breathable and sweat-wicking. I’ve skied in them from about 5°F to 55°F, and they’ve been great in all conditions.”
Best lightweight long underwear: Rab Syncrino Leggings
Material: 53% Polyester (32% recycled), 47% Merino Wool
Available sizes: S-XXL
Weight: 122 g (men’s large as tested)
Fly: No
What we liked: Lightweight, comfortable, good design, price
What we didn’t like: Thinness might lead to durability issues, a little loose at the ankles, no fly
There’s a lot to like in this lightweight offering from Great Britain’s Rab. At just $70, they offer a great value, thanks to the blend of synthetic and merino fibers. With a claimed weight of 125 grams/per square meter, they were the lightest weight and thinnest long johns we tested by far. We took these out in December in Colorado when temperatures were consistently a bit warmer on some backcountry trips to Berthoud Pass.
They performed well under a backcountry bib, and we didn’t need to vent them to dump heat even when the temps were melting the little coverage we had. This is a pair of base layer bottoms that we’d only wear on warmer hiking days or during continuous high-output activities like skimo racing (which we’re not in shape for at the moment).
RAB SYNCRINO LEGGINGS
We like the style of these bottoms. The majority of samples tested and that we see in stores are black, leading us to believe most base layer makers have the same ethos as Henry Ford’s take on painting Model T’s “any color as long as it’s black.” Our sample from Rab was blue with an olive-colored waistband. We’re still not gonna parade around town in these but it was nice to see some different colors out there.
While almost all of the companies we tested samples from, Rab is doing a lot of work to make sure its clothes are sustainable and that they’re transparent with customers about the makeup of their goods. With these, we really appreciated the minimal packaging, which was simply a brown paper bag with a cutout so you can see the color (other companies take note!), as well as the “Material Facts” panel that Rab has on its site and via a QR code on the bag. The panel resembles “Nutrition Facts” panels on most food and drug items and explains clearly and quickly where the synthetic materials come from and some of the chemical information about them.
With the thinness of the fabric and the use of synthetics, as well as wool, these were some of the quickest drying samples we tested. However, that thinness also comes with a side worry about the durability and warmth in very cold weather.
Under heavy and continual testing we’d anticipate that these will wear out quicker than other options. It’s a concern one reviewer on Rab’s site addressed: “These were great the first year, light weight, warm enough and good fit. I’m 2 years in they’re thread bare and tear easily. Disappointing.”
However, all other reviews of them on the site are glowing (we didn’t find professional reviews of them) and most buyers gushed about them, like this one: “Great lightweight base layer. I own several different base layers but I probably wear these the most. They are warm when you need them to be but still breathable and don’t make me too hot when engaged in strenuous activities.”
Best heavyweight long underwear: Ibex Woolies 2 Bottoms
Material: Merino
Available sizes: S-XXL
Weight: 208 g (men’s medium as tested)
Fly: Yes
What we liked: Very comfortable, durable, fly, nice color options
What we didn’t like: Thicker, slower to dry, heavier than other options, harder to find in stores
We’re a big fan of Ibex’s merino — it’s up there with the softest we’ve tested and is comparable to Icebreaker in terms of comfort. It was one of our top picks for best base layer tops and these bottoms are great as well. They offer a compelling option for a cold weather base layer at a great price. Since Ibex disappeared from the shelves for a while and then went through an ownership change and a massive rebranding, it’s now a smaller merino company, but one we think is worth checking out—even if it’s a little harder to find in stores.
These are among the heaviest long undies we tested at 240 gsm and are the ones we grab every time we know we are going to the resort in the coldest, windiest conditions. The Icebreaker ZoneKnit leggings are technically heavier at 260 gsm, but uses lighter ZoneKnit fabric in high-sweat areas making them lighter overall. But these are the base layer we’d grab on days when the mercury might reach 25℉—if we were lucky—and we were in the snow globe of a Loveland Ski Area squall. They also fit just well enough you might find us in them at home watching a snowstorm fall outside with a cup of hot chocolate.
IBEX WOOLIES 2 BOTTOMS
We’ve actually had these for a few seasons now—before we were testing them in earnest—and have also worn them on countless cold nights of pedicabbing in Denver, waiting 20 or minutes in the cold without moving much and enjoying the warmth they provide while other pedicabbers were stomping their legs to keep warm. They’ve held up well being worn and washed too many times to count and we didn’t feel the need to order a new pair for testing.
While we found that elastic fabric waistbands generally do a better job of keeping bottoms up, the Ibex Woolies 2 stayed up well even though the elastic is wrapped in merino. We also appreciate the pouch fly for convenience.
With the thicker weight of the wool, you definitely notice that you’re wearing these more than others. They also take longer to dry than thinner merino pieces, but all in all, these are a great pair of base layer bottoms for cold weather.
Sadly, we haven’t seen other professional reviews of these great bottoms, but we think they’re definitely worth the investment, and their fans agree. For instance, one customer remarked: “The best long underwear made! Have used Ibex products since their conception here in Vermont. Happy to see they are back and producing a lot of the original clothing that they had previously.”
Best technical long underwear: Artilect Flatiron 185 Legging
Material: 91% Superfine Nuyarn merino wool, 9% Nylon
Available sizes: XS-XXL
Fly: No
Weight: 174 g (men’s medium as tested)
What we liked: Great use of technical merino and venting, good fit and waistband
What we didn’t like: Not as soft as other merino, no pouch fly
We received one of the first pairs of Artilect’s base layer bottoms when they first seeded them to the press three years ago. At the time, they were one of a very few base layers we had. Since then, we’ve worn the initial pair ice climbing in Ouray, Lake City, near Creede, and other spots.
We’ve also worn them on countless backcountry excursions and lift days on Colorado’s Front Range and during cold nights of pedicabbing. We’ve never once regretted choosing them as our base layer, but we have started to see significant wear and tear (poking them with a crampon by mistake didn’t help), including holes. So we opted to test a newer pair for this season.
ARTILECT FLATIRON 185 LEGGING
Like the Icebreaker ZoneKnit leggings we tested, the Artilect has body mapped, merino mesh panels to help vent excess sweat and heat from areas where you’re more likely to sweat, like your lower back. It also uses different panels throughout to help with durability. Unlike the ZoneKnit, Artilect uses Nuyarn merino wool throughout their line of wool clothing. That blends wool with nylon to enhance the qualities of both. We’d also dare to say in our testing the 185-weight fabric did prove to be warmer than the Icebreaker 200 Oasis and better at wicking sweat than some other options.
We did notice, however, that Aritlect has made changes since its first iteration, including removing the pouch fly, which we didn’t appreciate. While the Flatirons were comfortable and fit well, they weren’t as soft as the pieces from Icebreaker and Ibex.
Still, the small, Colorado-based company is making compelling, interesting clothes, including one of our favorite pairs of snow pants, and this very good base layer that works in a wide range of temperatures. As such, it should be no surprise that it won an Editors’ Choice award from Backcountry Magazine. In its review, its testers noted: “The fabric shines...Superior warmth-to-weight and moisture management.”
Other men’s long underwear we tested
Smartwool Classic All-Season Merino Base Layer Bottoms
Material: 88% Merino Wool, 12% Nylon
Available sizes: S-XXL (also available in a 3/4 length)
Weight: 146 g (men’s medium as tested)
Fly: Yes
What we liked: Good comfort, lightweight, fly
What we didn’t like: Not as soft as other options, waist didn’t stay up as well as others, stitching a little rough
These were a good pair of base layer bottoms from one of the companies that really popularized merino in the US. We thought they were pretty comfortable and offered a good value at $90, compared to some other options. We also appreciate that Smartwool uses ZQ-certified wool, a certification we discuss below.
SMARTWOOL CLASSIC ALL SEASON
However, in the end, the stitching, despite using a flat seam, was more noticeable against the skin than other options, and the wool wasn’t as soft as that of Icebreaker. When considering it for a lightweight legging against the Rab syncrino leggings, the latter offered both a better price and lighter weight.
Material: 100% merino wool
Available sizes: XS-XXL
Weight: 156 g (men’s medium as tested)
Fly: No
What we liked: Simple 3-panel design, lightweight
What we didn’t like: Scratchier than other options, no fly
The Fjallraven Bergtagen Thinwool Long Johns are a pair of bottoms that we’ve had for years. They perform well and have maintained their shape. We also like the simple, three-panel design. However, we find that the wool in them is less comfortable than other options and that they tend to fall down more than options. While we appreciate the simple construction, it also makes it impossible to include a fly, which we’d prefer.
FJALLRAVEN BERGTAGEN THINWOOL LONG JOHNS
Material: 68% Viscose, 27% Merino Wool 5% Elastane
Available sizes: S-XXL
Weight: 128 g (men’s medium as tested)
Fly: No
What we liked: Mix of wool and bamboo fibers is soft, 3-panel design, 3/4 length is great for skiing
What we didn’t like: Didn’t retain shape as well, no fly
The ¾-length Bambool BT1 Base Layer Pants l are a comfortable pair of short leggings designed to work with ski boots. The mix of bamboo fibers with the wool is intended to make the leggings less uncomfortable for those who still think wool is too itchy and they are indeed extremely soft to the touch. However, they aren’t as warm as most other options and they haven’t retained their shape as well as other pairs we tested. Also, they lack any advanced features like a fly.
BAMBOOL BT1 BASE LAYER PANTS
Why you need long underwear
Testing base layer bottoms at Jones Pass on a day when temperatures dropped from about 40 degrees to about 20 degrees over the span of an hour. Photo courtesy Chris Meehan.
You need long underwear for cold weather outdoor activities, especially those when you anticipate moving a lot and needing something that will insulate without sweating out and don’t want to wear heavier insulated pants or bibs. They’re also great for chores or working outside.
Benefits of long underwear
By providing a thin layer of insulation under a pair of pants or ski bibs you don’t add a lot of weight or bulk to your clothing. That means you don’t lose flexibility like you might with insulated pants or bibs.
Layering for outdoor activities
Long johns are part of any good layering strategy for outdoor winter activities where you’ll be in temperatures under freezing. Light long johns are also nice to have as a layer under pants in slightly warmer temperatures as well. For varying conditions it’s best to wear them with a pair of pants or bibs with adequate ventilation zippers in case you do get too hot. Check out our recommendations in our Best Men’s Ski Pants guide.
Versatility for various activities
Long underwear is ideal for all your favorite winter outdoor activities like skiing, snowboarding, snowshoeing, hiking, mountaineering, ice climbing, ice skating, biking, and more. They’re not quite as versatile as base layer tops since you’ll find yourself wearing a base layer top on a chilly night camping, but base layer bottoms you probably won’t want to wear until you’re in temperatures consistently under 40℉.
What to look for in long underwear
Material
The overwhelming majority of base layers we recommend are made of merino wool. We’ve found it’s the best for insulation (even when wet), thinness, natural odor resistance, and, as woven in base layers, the fabric has a lot of innate elasticity.
You’ll also find some base layers with merino blends where the wool yarns are mixed with plant-based fibers, like modal or lyocell fibers, nylons, polyesters, and elastic fibers like spandex or elastane. These add additional properties to the long johns, including additional resiliency and longevity, softer hand (feel to the touch), and compression in some cases.
One of the most popular alternative materials for vegans and those (like my parents) who still think wool is too itchy, are polyester base layers, like Patagonia’s long-running Capilene line of products.
Why Wool?
Two wool base layers from Icebreaker side-by-side. Photo courtesy Chris Meehan.
Wool is a great insulator. The majority of wool base layers available today are made with merino wool, which is sheep wool. However, companies are using wool or fleece from other animals, like alpaca and sometimes yaks to make base layers. Why are they so good? Evolution.
Over millions of years certain mammals developed a fleecy coating that keeps them warm even through tough, wet winters, springs, and falls. They developed a material that is insulating—even when wet—as well as moisture wicking and odor-repelling. Companies can harvest it without killing the animal and the animal can regrow it.
The softest, least itchy wool generally comes from the finest of wool fibers. We’ve found Icebreaker makes some of the softest wool pieces out there and it uses fibers as fine as 15 microns. Ibex uses fibers as fine as 17.5 microns in some of its clothes, making them remarkably soft as well.
With comparatively minimal processing and treatment the wool fleece is converted into yarns and fabrics. Modern merino and other wool base layers are soft to the touch, even next to the skin, and excellent at moving sweat from the skin outward. They’re also great at insulating even when wet and their anti-odor properties are better than treatments applied to synthetic fibers. All of this means a wool base layer is a piece you can wear for days between washings even if you’ve gotten heavily sweaty in it.
When the animals producing the wool are well cared for, it’s not just a sustainable choice but one that’s making great use of a natural resource. When considering wool base layers, look for companies that source wool with the Responsible Wool Standard and/or ZQ Natural Fibre certifications, as these companies are taking extra steps to make sure the wool is produced in a humane and sustainable manner. You can read more about certifications in our sustainability and ethics section.
Why wool blends?
A closeup of the wool/synthetic blend of the Rab Syncrino leggings. Photo courtesy Chris Meehan.
The chief criticisms of wool are that it’s more expensive than synthetics and that it’s more prone to wearing out quicker. We’d dare to say this is more a problem with tops than bottoms because people are more likely to wear a base layer top as an exterior piece that can get snagged on trees, rocks, or whatever, than a base layer bottom, which is usually worn under a pant or shell and less often with shorts.
However, wool blends take advantage of the best properties of wool — its sweat-wicking, insulating, and anti-odor properties — and mate that with best properties of other materials, like the durability of a nylon or polyester fiber. NuYarn fabrics do this, and the brand CEP even creates a spandex-like compression quality with their base layers. Icebreaker uses modal or lyocell fiber, like Tercel, in some of its wool blended clothes, which are made from plants and trees.
In the end, with blends you can get a more durable base layer with the desired features of a wool-only base layer for less or a similar cost. In some cases, like Icebreaker’s 260 ZoneKnit Merino Thermal Leggings or Smartwool’s Intraknit Thermal the costs are higher because they’re using the materials to make a thinner or more porous fabric that breathes even better than pure wool fabrics.
Why synthetics?
A closeup of the synthetic Capilene fabric of the Patagonia leggings. Photo courtesy Chris Meehan.
For those who have allergies or experience itchiness even when wearing even the softest merino or alpaca fabrics, vegans who refuse to wear any animal product, and people who are looking for a sometimes less-expensive alternative base layer, synthetics are a great option. They’re also a great option for profuse sweaters, as synthetic fabrics can be designed to wick sweat and moisture away from the body and to dry quicker than wool.
Synthetic fabrics like nylon and polyester are oftentimes more durable than pure wool fabrics. They’re also usually cheaper to produce. However, traditionally they’re made from petroleum products and require more processing and treatments to make into a base layer, including what’s usually a chemical treatment to reduce their odor-retaining properties—and they never seem to retain good odors. In the past few years we’ve seen more and more companies use recycled synthetic fabrics, like Patagonia’s 100 percent recycled Capilene polyester, which is a positive move toward sustainability, but still comes from that original petroleum product and may contribute to the microplastics problem at end of life.
Synthetic layers aren’t always as soft as wool, either. This is especially true after wearing them in particularly sweaty situations where salt crystals from sweat may be retained on the fabric between washings. But the biggest drawback to synthetics, other than the petroleum feedstock, is odor retention. Even though many synthetic base layers have an anti-odor treatment, which sometimes includes silver or other bluesign-approved materials like HeiQ, they still seem to retain more odors than wool—even after washing or multiple washings. Nature just seems better at it.
Why not cotton?
It’s just not a good insulator or effective moisture wicker. And that’s also because of evolution. The natural purpose of cotton is to help cotton seeds germinate, a process helped by keeping the seeds wet and making them heavy so that they’ll drop from the branch to the ground where they can sprout and take root. As such, cotton’s purpose is not to insulate from moisture as much as it is to retain it. While it’s suitable for many clothes, and we love it, it’s just not the best for a base layer that needs to keep you warm.
Insulation and thickness
Caption: A close of up of the difference in thickness between the Icebreaker 260 Tech Thermal Leggings (L) and the Icebreaker Oasis 200 (R). The yarns on the 260 are visibly thicker. Photo courtesy Chris Meehan.
The thicker the base layer usually means it provides more insulation. Still, the thickest base layer bottoms we tested, the Icebreaker Merino 260 Tech Thermal Leggings With Fly, are perhaps just over a millimeter thick and had a weight rating of 260 grams per meter. These bottoms are meant for very cold days and will insulate well under just a shell when skiing, snowboarding, in temperatures well below freezing.
The thinnest we tested were the Rab Syncrino Leggings, which have a weight of 125 grams per meter. These are almost gossamer and meant for warmer days, even for those days when the mercury tips above 40℉ and you’re not doing the highest output activities.
The majority of base layer bottoms we tested were men’s mediums and the actual differences in weight ranged from 122 grams for the Rab Synchrino Leggings to 230 grams for the Icebreaker 260 Tech Thermal Leggings. We couldn’t find the weight rating for some of the other pieces we tested, like the Patagonia Capilene. But our test sample weighed 170 grams, a couple hairs less than the Icebreaker Oasis 200’s, which weighed in at 178 grams.
Moisture-wicking and breathability
Beyond insulating, the thickness of a base layer also impacts its moisture-wicking and breathability capabilities. Though wool and synthetic fabrics do a great job of wicking, the thicker they are means the denser the fabric and wicking and breathability are impacted.
Moisture wicking and breathability are paramount to good base layer bottoms. They move your sweat from your skin to the outer surface of the fabric where it can evaporate while still providing insulation below.
All of the base layers provided good wicking and breathability when used in the right temperatures. We wouldn’t recommend using the Rab Synchrino on a 0℉ day, nor would we recommend using the Icebreaker 260 on a 45°F day.
The base layers with the biggest range of temperature capabilities were pieces like the Icebreaker 260 ZoneKnit Merino Thermal Leggings and the Artilect Flatiron 185 legging. These blended panels of different thicknesses throughout the base layer to provide more wicking and breathability in areas where people are most likely to sweat. They work well at letting off heat and we’re more likely to choose those base layers on a day when temperatures will swing widely from below freezing to above.
Fit
Unlike base layer tops, which are sometimes worn as outerwear, base layer bottoms are generally designed like a boxer brief with next to skin fit throughout. The only real outlier was the Patagonia Capilene, which wore a little more like a pajama bottom—slightly loose around the calves and thighs but with tighter ankle cuffs. The rest were next to skin, showing off our calves and thighs well, but definitely not clothes we’d wear around in public without something over them.
Design and features
The fly pouch on the Ibex Woolies 2 is a design feature we appreciate in a pair of men’s base layer bottoms. Photo courtesy Chris Meehan.
The design and features of men’s base layer bottoms are pretty similar in terms of style. They’re designed to move with the lower body, not be bulky under other clothes and be comfortable next to the skin. As such, all models tested used flatlock seams that reduce the chance of chafing or rubbing.
The simplest of the base layer bottoms tested were the Fjallraven Bergtagen Thinwool Long Johns, which only had 3 panels—front, back gusseted crotch. The most complicated designs, like the Artilect Flatiron 185 had 14 panels, which included thicker and lighter weight panels—including some mesh panels for body-mapped breathability.
Crotch
The simplest designs, like the Bergtagen didn’t have much in the way of comfort in a crotch pouch. We preferred those models that did have a crotch pouch more. We also appreciated those models with a fly that allowed us to relieve ourselves without having to pull the waistband down under our shell, particularly when wearing bibs.
Length
The majority of long johns we tested were ankle length. Some companies offer a short or 3/4 length bottom designed with skiers and snowboarders in mind. The shorter length is meant to make sure the bottoms don’t add bulk underneath ski socks and high-cuffed ski or snowboard boots when worn very tight. That said, we had no issues with full-length bottoms under our ski socks and boots, save for when we brought them down around our ankles for, you know what…
Waistband
The only other real feature any of the base layer bottoms had was the waistband. While some wrapped the elastic waistband in the wool fabric, like the Ibex Woolies 2, others, like the Icebreaker long undies had a fabric elastic band against the skin. In testing we found the latter did a slightly better job of staying in place than wool-faced counterparts.
Color
The majority of base layer bottoms we tested were black and, at least in men’s base layer bottoms, that’s the prevailing color. Some, like Rab’s Synchrino Leggings and Patagonia’s Capilene, were in blues and the ZoneKnit Thermal Leggings from Icebreaker were orange, but the majority are offered in black and sometimes in a few other basic colors.
Durability
Our first pair of Arilect leggings atop the newer pair. After over a hundred washings and countless more wearings, the older pair still retains its shape well. Photo courtesy Chris Meehan.
This is the supposed Achilles heel of merino and we can attest we’ve put our fair share of holes in our base layers over the years. But despite the holes in older pairs, they still insulate well and provide all the other benefits we need them to.
Wools blended with synthetic materials provide more durability and synthetic base layers are usually thought to provide the greatest durability. We haven’t put our Patagonia Capilene leggings through enough testing yet to find out. But, with other synthetic base layer tops, including the cousin of base layers—sun shirts—we’ve found they have snagged on things as much as some of their wool counterparts, resulting in holes in the first or second day of wearing them.
The initial pair of Artilect base layers we had (before testing) with NuYarn technology in them have seen well over 100 wears, including as a warmth layer while pedicabbing in winter months, being stretched repeatedly over a bike seat for up to 10 hours at time—definitely not what they were primarily designed for. They’ve definitely gotten a few holes in them over that time period, but they also saw almost as much wear as some of our favorite jeans—KUHL Denims, which are also starting to show some fraying around the seams.
Sizing
With base layers you generally want them close to skin as that’s when they’ll do the best job of insulating and using their breathability and wicking properties the best. However, unless you’re looking for a pair of compressive base layers, like those offered by CEP, you want them to be tight, but not compressive or constrictive. Getting a normal base layer bottom sized down for compression will only lead to discomfort and quicker wear and tear on the fabric and seams.
Men’s leggings are available in a wide range of sizes, ranging XS to XXL from some vendors. An XS will have a waist of 27” or so and an XXL will have a waist of around 44”. Unlike men’s pants, not all companies offer inseam lengths for their base layer bottoms. We’re pleased to see, however, that multiple companies, including Icebreaker, SmartWool, Artilect and Ibex, offer a wide range of sizes. A couple companies, including Fjallraven and REI also offer a XXXL with a waist up to 50”.
Odor resistance
Yes, you’ll be wearing base layer bottoms like this occasionally and it’s important that they stay up after this type of use. Photo courtesy Chris Meehan.
Growing up under the Appalachian Mountains in Maryland in a rural town, and having worked on farms and even attended events where we packed raw wool into giant 12-foot tall bags by jumping and stomping on it, I can tell you, raw wool doesn’t smell great. We couldn’t get the lanolin oils out of pants, t-shirts, and shoes in the late 80’s, and the host of other smells from living in the fields and doing what animals do in those fields stuck with the wool. So it’s particularly amazing to me how great modern wool base layers are resisting odors.
I’ve worn the same wool shirt for seven days straight and while it got a little odorous, it still resisted odor better than any synthetic shirt I’ve worn for even two days straight, despite whatever treatment was used on the synthetic shirt. Moreover, after washing wool still does much better at remaining odor resistant.
Ease of care
Base layers are safe to wash in washing machines. For the best results most manufacturers recommend washing them on a cold cycle (Patagonia recommends warm for their Capilene). We also recommend using a good sports detergent, especially if there’s a problem with odor retention.
While it’s best to let them hang dry as almost all companies recommend, we often tumble dry them with other clothes on low. Unlike George Constanza we haven’t experienced any problems with shrinkage—even with the merino wool pieces.
Versatility for activities
We love base layer bottoms, but they’re not quite as versatile as base layer tops. While we’ll wear them for everything outdoors in the winter: doing chores, hiking, snow biking, ice climbing, mountaineering, snowshoeing, skiing, and snowboarding, we don’t usually wear them for running or trail running and rather opt for a running pant or running tight. That’s because they’re not designed for any wind resistance or water resistance, and even the best, warmest base layer bottoms will wet out if you stomp in a puddle and splash icy water over them.
How different base layers we tested arrived. From L-R most to least sustainable. Photo courtesy Chris Meehan.
Sustainability/Ethicality
Normally we’d probably just talk about sustainability here, but since most of our favorite picks are made of material sourced from animals, we think it’s important to mention both when considering base layers. As we continue to report and see, the outdoor industry is working to make its products both more sustainable and ethical. It’s a good thing and we’ll keep covering it to help ensure companies know we’re interested and want to help move the needle toward more sustainable and ethically-sourced threads.
One of the most interesting things is that the only base layer sample we got that came in a plastic bag was from SmartWool. The rest were packaged in more sustainable, easily recyclable methods, like small boxes (Icebreaker and Artilect) or a paper bag (Rab). Some were shipped loosely in a bag or box. We appreciate the more thoughtful packaging and hope to see less plastic bags in the future.
When it comes to wool, we want to make sure that our insulation makers are as happy as possible between shearings. As such, we’re looking for pieces that come from companies who are sourcing their wool from farmers that take care of their flocks. As such we prefer brands that are using the Textile Exchange’s Responsible Wool Standard (RWS) certification and/or ZQ certified wool. Both standards ensure the sheep that are producing the wool are well-cared for as well as the land they graze on. They offer traceability of the wool as well. Icebreaker, SmartWool, Helly Hansen, and Fjallraven are examples of brands that use ZQ-certified wool. Ibex uses RWS wool. Rab and Artliect say they use non-mulesed, humanely-sourced You can read more about certifications in our sustainability and ethics section.
Icebreaker also says that as of 2023 its fabrics are 96.14% plastic-free and it plans to reduce the use of plastics (like nylon and polyester) more in the future. Rather than use a nylon blend to strengthen its wool blends, it uses plant-based fibers from Tencel. We also know that Ibex has used natural-based dyes in some garments in the past. All of these are examples of how wool base layer makers are making more sustainable and ethical choices.
Patagonia has long been revered as an environmental leader in the outdoor industry as well. Its Capilene base layers are made with 100 percent-recycled plastic and the company is a partner with Repreve, which makes these increasingly popular yarns. We’re not sure if Patagonia is making the Capilene from plastics recycled from bottles or other sources, but have asked and will update when that information is available.
To learn more about how sustainable a company is, we recommend looking for their sustainability reports.
Buying advice
Getting help with testing base layers from Preacher Steve, while wearing the Rab Synchrino leggings and writing. Photo courtesy Chris Meehan.
The following are questions you should ask yourself before purchasing underwear. Your answers will point you in the right direction of which models will serve you best.
What activity or activities are you buying the long underwear for?
You'll want long underwear primarily for cold-weather, outdoor activities. Having a great pair of long underwear is great for everything from doing chores to hiking, mountaineering, winter backpacking, hut trips, skiing, snowboarding, ice climbing, pond skating, snowshoeing, and other winter outdoor activities where you need an insulating layer to keep your legs warm.
What specific weather conditions will you be facing during your outdoor activities?
Consider how cold it will get when you're out there. Pretty much when temperatures dip towards freezing and below, you'll want long underwear. For people who run cold they might want to wear them in temperatures closer to the 40s when doing lower impact activities and pants alone won’t do.
Do you prefer the natural insulation of merino wool or the quick-drying properties of synthetic fabrics?
Personally I prefer the natural insulation of merino wool. It wicks sweat well, stays warm even when wet and does a superior job at resisting odor. Also, there’s just something I like about the idea that wool is a renewable resource. However, if you're vegan or find even the softest merino wool to be scratchy, you may want a synthetic option.
Care and maintenance tips
As usual, we recommend following the manufacturer’s care instructions as explained above. However, there are some places where we diverge from their recommendations. For instance, in the winter, we’ll sometimes use a plant-based fabric softener when washing them (It’s not recommended because fabric softeners can leave a film on yarns), but it keeps the static cling and static shock down, which is nice.
While we never recommend drying clothes on high — it can cause some synthetics to melt and can cause wool to shrink — we do think it’s ok to dry some merino on low. For instance, if you’ve noticed a wool base layer is looser than it used to be after multiple wearings, a tumble dry will help it return to shape.
If you do manage to shrink a wool base layer by mistake, you can try these steps to reverse it. We won’t guarantee it works every time.
FAQ
Skinning up while testing long undies at Jones Pass. Photo courtesy Chris Meehan.
Can I wear long underwear in warmer weather?
You can if you’d like. But remember the primary purpose of long underwear is insulation from the cold. It won’t insulate you from the heat as well.
How do I prevent long underwear from becoming too hot or sweaty?
You can prevent long underwear from getting hot or sweaty by wearing the right long underwear for the right conditions. We wouldn’t recommend a heavyweight pair of long underwear (over 200 gsm) on a warmer day when temperatures are above freezing. If you do find yourself in that situation, we’d recommend opening vents on your snow pants or adventure pants, or take them off.
Can I wear long underwear for multiple days during a trip?
Yes. You should be able to wear them for multiple days, the anti-odor capabilities should keep them from becoming too rank to wear. But most, especially wool long johns, can be rinsed out and still lose many of any scents that were lingering without a full wash.
Should I wear underwear under long johns?
I don’t think so, but that’s really up to the wearer. I think it’s enough to have to fiddle with the fly on one pair of undies, let alone a second pair underneath the other layers you’re wearing in the winter. Plus, a second pair of undies will make it harder to expel heat from your waist and crotch, leading to uncomfortable sweating in a sensitive area.
Why do I need different pairs of base layer bottoms?
The short answer is balancing your warmth needs with your sweating. When you’re out doing a high-energy activity like backcountry skiing or mountaineering, you’re putting out a lot more consistent energy, heat, and perspiration than when you’re skiing or snowboarding at a resort.
Yes, your heart beats out barbaric yawps of happiness with every turn, whompf, and jump at the resort on a powder day, heating you up at least a little on the downhill. But on those days you’re really wearing a base layer for those long, cold rides up in the chairlift where you might be pummeled by wind, swinging 20-30 feet above the powdery blanket below.
How we researched and tested
We’ve been wearing modern long underwear in the winter for the last 15 years or so. So when this opportunity to test long underwear came, we were well prepared and were able to rely on past experiences and take on new ones.
We scoured the web for the best base layer bottoms according to other gear review sites and magazines including Gear Junkie, Outdoor Gear Lab, Outside Magazine, Switchback Traveler, CleverHiker, and even consulted with our own piece on Base Layer tops. We also checked customer reviews of highly rated models and consulted with our fellow adventure buddies and outdoor writers about their favorite picks.
In the end we considered more than 24 models and ended up narrowing that down to 10 pairs of men’s long johns to test in this round of testing. We made sure we got out in each pair at least three times and in the type of elements and weather best suited for each. For instance, we used the light Rab Syncrino bottoms on days when the temperatures rose to freezing while doing high activity adventures and wore the heavier Ibex Woolies 2 on colder days on the lifts.
Since starting testing in late November, we’ve gotten out as much as possible in Colorado and Utah’s snowy peaks to test out men’s base layer bottoms. We’ve taken them on overnight trips to Broome Hut, out on the incredible Ski Utah Interconnect Tour, where we traveled backcountry between six resorts. We’ve worn them on backcountry missions to Berthoud Pass and Jones Pass. At Colorado ski resorts including Keystone with SOS Outreach, Eldora, Loveland Ski Area, the nation’s longest-running ski area—Howelson Hill, and SnoGo Biking at Winter Park.
We also tested them while driving the first electric Ski-Doo snowmobiles, taking an intensely fun winter driving class with Bridgestone and going ice climbing at Lincoln Falls—all since December 2023. We also tested them on numerous nights of pedicabbing in subfreezing temperatures, as on New Year’s Eve, large shows at Denver’s Ball Arena and during the all-too-short Denver Broncos season.
About the author / Why you should trust us
Backcountry skiing in the Rab Syncrinos on a day when temperatures changed more than expected. Photo courtesy Chris Meehan.
As someone who’s active year-round, changing activities with the seasons, I’ve relied on modern base layers for winter warmth for well over 15 years. As the mercury drops and I put on the crampons/skis/snowshoes, I almost always reach for a pair of base layer bottoms to keep my legs from getting too cold and too sweaty. I’ve had a number of go-to base layer bottoms in the past, so I already knew what elements are the most important in a good pair of long johns and why you should choose one pair over the other and for what conditions.
I’m an outdoors writer covering adventure and gear, who writes regularly about the outdoors and I enjoy outdoor activities all year round, including skiing on the slopes and backcountry, snowshoeing, and ice climbing. I’ve authored numerous gear guides for Treeline Review, write for Popular Mechanics, Bicycling Magazine, Popular Science, Backpacker, and other outdoor publications/organizations.
I have authored multiple outdoor guidebooks. My most recent Falcon Guide, "Colorado’s Best Front Range Adventures: The Greatest Hiking, Climbing, Paddling and More From Denver to Colorado Springs and Fort Collins," arrived in Spring 2021. In it, I cover the best hiking, biking, climbing, and rafting in the region. I’m also the author of Falcon Guide’s “Climbing Colorado's Fourteeners: From the Easiest Hikes to the Most Challenging Climbs” and edited Justin Lichter’s excellent guide to thru-hiking titled “Trail Tested: A Thru-Hiker's Guide To Ultralight Hiking And Backpacking.” All of this experience has helped me become a first-rate gearhead and product tester.
Overall, I have 20-plus years of exploring, skiing, climbing, mountain biking, hiking, backpacking, guiding, and playing in the wild. I worked with National Geographic and their mapping division in developing their Colorado 14ers Map Pack Bundle. I’ve written about hiking and climbing for Elevation Outdoors, including stories about Colorado 14ers and outdoor apps to boost adventures.
I’ve written about countless outdoor companies, outdoor sports, and tested gear with publications including CompanyWeek, Outdoor USA Magazine (print), Elevation Outdoors, 5280, and more.
At Treeline Review, we strive to offer unbiased reviews to help you find the best product for the price. Treeline Review doesn’t accept sponsored content, native advertising, or paid reviews. I am not sponsored by any companies, nor are any of my family members sponsored by, employees of, or ambassadors of any of the companies in this review.
The author previously wrote about the best men’s snow pants for Popular Mechanics, where he has also covered other winter outerwear.
The author, nor anyone in his family is not sponsored, an ambassador, or an employee of any of the companies here. Our reviews are unbiased and we do this to help you find the best product for the price. Treeline Review doesn’t accept sponsored content, native advertising, or paid reviews.
