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The Best 6 Long Underwear of 2024

We put men's long underwear to the test from brands like Smartwool, REI, Icebreaker, Patagonia, and others to find the best and warmest options on the market
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Best Long Underwear Review
Credit: Justin Simoni
By Justin Simoni and Aaron Rice  ⋅  Nov 23, 2024

The Best Long Underwear for 2024


Need new long underwear bottoms? We've been testing them for over a decade and showcase 16 of the best options in this review. Our team of experts spent months, in every season, taking these layers on river trips, ski slopes, and cold winter trail runs. We backed up our field research with objective, lab-style tests designed to analyze specific features of each pair of long johns.

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

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

Editor's Note: We updated this review on November 23, 2024, to add more information on our award recommendations.

Related: Best Long Underwear for Women

Top 16 Long Underwear

Displaying 1 - 16 (scroll right)
 
Awards Best Buy Award
Best Synthetic Bang for the Buck
Top Pick Award
Our Favorite 3/4 Length
 Editors' Choice Award
Best Overall Long Underwear for Men
  Top Pick Award
Best Lightweight Long Underwear
Top Pick Award
Best Midweight
  Best Buy Award
Merino Wool on a Budget
     
Price $55 List
$38.39 at REI
$114.95 at Amazon
Compare at 3 sellers
$59.00 at Backcountry$82.50 at Evo
Compare at 4 sellers
$59.37 at Amazon$109.95 at Backcountry$120 List
$120.00 at REI
$80 List
$79.99 at Amazon
$80 List
$55.89 at REI
$78.69 at REI$60 List
$59.99 at Amazon
$40 List
$27.93 at REI
$81.43 at Amazon$30 List
$19.99 at Amazon
$40 List
$31.99 at Amazon
$79.99 at REI
Overall Score
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Pros Tough synthetic fabric, four-way stretch for great range of motion, excellent performance for the priceShorter length reduces bunching near ankles, seamless panels provide additional articulation and ventilation only where needed, high waist and thick waistband keeps bottoms in place100% recycled polyester, light fabric weight, impressive loft and warmthA nice balance of warmth and breathability, super cozy, nicely articulated designBreathable, highly efficient wicking, comfortable Merino/recycled polyester blend, impressively durableAthletic fit hugs body for great breathability, extra wide waistband keeps layer in place, stretchy wool blend materialExtremely breathable, ultralight stretchy nylon/Merino wool blendSoft and stretchy wool fabric, super cozy and warm, high waist and tall ankle cuffsExcellent warmth for the weight, perfect for summer nights, simple design stays out of the way, gusseted crotchGood warmth to weight ratio, breathable 100% wool fabric, durable, comfortable gusseted crotch designAffordable intro to Merino, warm and cozy, wide spectrum of available sizesUnbeatable price, breathable, quick drying, functionalWarm, lightweight, breathable, versatile, comfortable, great thermoregulationAffordable, nice thick waistband, extremely stretchy synthetic materialInexpensive, lightweight, quick-dryingFun colors and patterns, soft and comfy 100% Merino wool, thick and supportive waistband, 3/4 length is warm for the weight
Cons Heavier than wool bottoms for their warmthNo-fly design could be inconvenient underneath other layers, fit may be too tight for some body types, priceyQuestionable durability, saggy bottomExpensive, stretches out in between washes, slow to dry when saturatedNot designed for mid-winter temps, relatively heavy for fabric weight, thin waist bandNot as warm as the material weight suggests, tight athletic fit may not appeal to everyonePrice may make you do a double-take, care instructions need to be followed when dryingLacking in durability, takes a long time to line dry, not as breathable as other optionsFabric is thin and not very durable, minimal cuffs are especially vulnerable to wear, fit tighter than mostWaistband not as tall as others, 100% wool is not as durable as blended fabrics, fabric will lose some of its stretch over time, potential to shrinkStarts off slightly itchy, simplified construction may not be as comfy, Merino wool is delicateShort cut legs, average comfort and warmthNot very durableSmall for the labeled size, fabric easily tears from minor abuse, obtrusive stitchingUncomfortably tight fit, pilling after a few washes, not very warm for the weightWool quickly becomes fuzzy, durability an issue for 100% Merino wool fabric
Bottom Line A great synthetic thermal long underwear at an unbeatable price for the warmth and durability they provideCarefully engineered 3/4 length thermals with compression pants-like tightness that’ll keep you warm and super comfortable while pursuing high output activitiesWarmer than most and lighter than the rest, this pair of long underwear redefines what is possible from a synthetic base layerDesigned to keep you warm in the coldest conditions, this is a versatile pair of Merino wool bottomsA versatile, lightweight Merino and recycled polyester blend that offers superb breathability and wicking, ideal for any fast-paced adventureAn excellent, breathable, mid-weight wool blended bottom, most attractive to those who can wear its athletic fitA seriously tuned ultralight pair of wool/nylon blend leggings built for fast and light outdoor adventuresFor wintry missions in the backcountry or hibernating deep inside a cabin, these soft, long bottoms are almost perfect for keeping legs extra toastyFor transitional spring nights, this lighter-weight pair of long bottoms works well to up the heat retention without getting too hotA solid pair of 100% wool leggings at a great weight for a wide spread of temperatures and conditionsGrab a pair of these if you are looking for an affordable and warm pair of Merino wool bottomsSlender and breathable, these are everything we expect out of a lightweight pair of long underwearA fantastic pair of lightweight Merino bottoms that provide impressive warmth without being too hot, breathe extremely well, and are very comfortableThis inexpensive set of base garments has a smooth exterior and fleecy interior, but we worry that they're not durable enough for serious everyday useA low-cost set of base garments will help keep you warmer, but we don't know if we'd rely on them to get us through the winter unscathedBeautiful and bold colors and patterns make these warm and plush 3/4 length long undies hard to forget
Rating Categories REI Co-op Midweight... Smartwool Intraknit... Patagonia Capilene... Smartwool Classic T... Outdoor Research Al... Mons Royale Cascade... Artilect Boulder 125 Minus33 Kancamagus... REI Co-op Merino 18... Icebreaker Merino 2... Meriwool Merino 250... REI Co-op Lightweig... Smartwool Classic A... WEERTI Thermal Flee... Thermajohn Thermal... Ortovox 185 Rock'N'...
Warmth (25%)
7.0
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Breathability (20%)
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Comfort and Fit (20%)
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Durability (15%) Sort Icon
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Drying Speed (10%)
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Layering Ability (10%)
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Specs REI Co-op Midweight... Smartwool Intraknit... Patagonia Capilene... Smartwool Classic T... Outdoor Research Al... Mons Royale Cascade... Artilect Boulder 125 Minus33 Kancamagus... REI Co-op Merino 18... Icebreaker Merino 2... Meriwool Merino 250... REI Co-op Lightweig... Smartwool Classic A... WEERTI Thermal Flee... Thermajohn Thermal... Ortovox 185 Rock'N'...
Measured Weight (Size Medium) 7.4 oz 9.2 oz 5.9 oz 8.3 oz 6.8 oz 5.5 oz 4.3 oz 8.9 oz 6.2 oz 6.5 oz 7.9 oz 5.5 oz 6.1 oz 6 oz 5.8 oz 5.4 oz
Material 92% recycled polyester, 8% spandex 54% Merino wool, 43% polyester, 2% elastane, 1% polyamide 100% recycled polyester with HeiQ Fresh 100% Merino wool 47% Merino wool, 47% recycled polyester, 6% spandex 81% Merino Wool, 12% nylon, 7% elastane Nuyarn: 85% Merino wool, 15% nylon 100% Merino wool 100% Merino wool 100% Merino wool 100% Merino wool 92% polyester, 8% spandex 88% Merino wool, 12% nylon core 92% polyester/ 8% spandex 92% polyester 8% spandex 100% Merino wool
Insulation Weight Class Midweight Lightweight Lightweight Midweight Lightweight Lightweight Lightweight Midweight Midweight Midweight Midweight Lightweight Lightweight Lightweight Lightweight Midweight
Odor Control Fabric None Naturally odor resistant HeiQ® Pure odor control Naturally odor resistant Naturally odor resistant Naturally odor resistant Naturally odor resistant Naturally odor resistant Naturally odor resistant Naturally odor resistant Naturally odor resistant None Naturally odor resistant None None Naturally odor resistant
3/4 Boot-Cut Available? No Yes No Yes No Yes Yes No No Yes No No Yes No No Yes
Fly? Yes No Yes Yes Yes No No No No Yes Yes Yes Yes No No No
Dryer Safe? Yes No Yes No No No No Yes Yes No No Yes No Yes Yes No
Listed Fabric Weight (g/m²) Not stated ~200 g/m² 147 g/m² 250 g/m² 150 g/m² 125 g/m² 235 g/m2 185 g/m² 180 g/m² 250 g/m² Not stated 150 g/m² Not stated Not stated 185 g/m²


Best Overall Long Underwear for Men


Smartwool Classic Thermal Merino Bottom


76
OVERALL
SCORE
  • Warmth 9.0
  • Breathability 7.0
  • Comfort and Fit 8.0
  • Durability 7.0
  • Drying Speed 6.0
  • Layering Ability 7.0
Materials: 100% Merino wool | Weight: 7.6 oz (size Medium)
REASONS TO BUY
Cozy and comfortable
Terrific thermoregulation
Merino wool-lined waistband
REASONS TO AVOID
Stretches out between washings
Expensive

We adore the Smartwool Classic Thermal Merino Bottom and have given it our top honors. This combined warmth and comfort of this long john are excellent when the temps really dip down. The special interlock knit provides exceptional breathability, especially considering the thick, 250 g/m² cut of the 100% Merino wool. You'll find rear gussets to match the front, enhancing comfort and fit. The extra-wide, wool-lined waistband and full-flatlock seams cut down on common complaints of itchiness. While these are designed specifically for cold conditions, their balance of warmth and breathability makes them versatile even when temperatures begin to warm up a bit.

Despite the thick construction — and indeed, these bottoms are one of the most durable all-natural layers we tested — all Merino layers require a certain level of care that goes above and beyond most articles of clothing. With regular use between washings, the Classic Thermal tends to stretch out, so you may find it tempting to throw them in the dryer to shrink them back up. But don't! Careful laundering and primarily flat or line air-drying will help improve the longevity of this and all Merino base layers. We know the laundering process can be annoying, but the excellent thermoregulation capability makes this pair well worth the extra effort, especially for those playing or working in frigid climates. If carefully laundering wool sounds like too much of a hassle, a synthetic option like the REI Co-op Midweight Bottoms may suit you better.

Read more: Smartwool Classic Thermal Merino Bottom review

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

Best Synthetic Bang for the Buck


REI Co-op Midweight Bottoms


73
OVERALL
SCORE
  • Warmth 7.0
  • Breathability 7.0
  • Comfort and Fit 7.0
  • Durability 9.0
  • Drying Speed 7.0
  • Layering Ability 7.0
Materials: 100% polyester | Weight: 7.4 oz (size Medium)
REASONS TO BUY
Withstands harsh use
Low-cost, high performance
Cozy four-way stretch fabric
REASONS TO AVOID
Not as warm for the weight as wool

Back from a total redesign, we're now even more impressed by the REI Co-op Midweight Bottoms as a value-driven, super tough, and no-nonsense pair of synthetic long undies. Our last critiques must have been heard at REI World Headquarters, as these long johns feature a much improved-upon four-way stretch 100% polyester fabric that we adore. The bombproof durability and warmth of the Midweight remain, as does the overall understated cut and design — which is snug but not athletically tight — a fit that we think works great for most people partaking in most activities. This pair is the warmest synthetic mid-layer we've tested, giving even some of the 200 g/m² thick 100% Merino wool long underwear a run for their money.

Since REI updated the Midweight Bottoms, there are even fewer attributes we can point to as weaknesses. This no-nonsense piece of gear gets the job done well enough and isn't looking to collect accolades. The performance is tough to beat, considering the price. If you're in the market for a warmer layer (and maybe a softer and comfier one), it would be time to reach for a wool option like the Smartwool Classic Thermal Merino Bottom and leave these for a milder day.

Read more: REI Co-op Midweight Bottoms review

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

Merino Wool on a Budget


Meriwool Merino 250 Bottom


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

Making 100% Merino Wool apparel approachable for the masses, enter the Meriwool Merino 250 Bottom. We appreciate the journeyman, no-nonsense construction, and super plush, cozy 100% Merino wool fabric of these affordable leggings. High-end features like an extra-comfortable waistband and well-thought-out ankle cuffs will make you double-take on the extremely fair price. These are excellent thermal bottoms to wear when temperatures really start to dip down.

Aside from the overall warmth and the value of getting a 100% Merino wool bottom at a steal of a price, there is not a whole lot about these bottoms that makes them stand out among the competition. But that's their charm: they're working behind the scenes (or underneath your pants) to ensure you stay comfortable in the cold without needing more fanfare. We should note there may be a wash-in period to get the ultra-fine Merino wool to soften up a smidge. So if you find the Merino 250 Bottom is somewhat itchy when you first wear them, wash them before bestowing your final judgment. If you'd rather go with a comfier option, we like the feel of the Artilect Boulder 125, which blends wool and stretchy nylon.

Read more: Meriwool Merino 250 Bottom review

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

Best Lightweight Long Underwear


Artilect Boulder 125


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

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

In step with its speed-over-everything analogy, the Boulder 125 isn't an all-rounder. Wear them when the weather is fairly mild, and swap them for something more substantial on those colder winter missions. The price for such a luxe pair of long underwear is also predictably higher than other options, but you get what you pay for. These are the long underwear we bring along to make sure our next outdoor adventure is the coziest and lightest we can possibly have. For colder conditions, reach for the Smartwool Classic Thermal Merino Bottom instead.

Read more: Artilect Boulder 125 review

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

Best Midweight


Minus33 Kancamagus Midweight Merino Wool Bottoms


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

Midweights are our favorite for cold days and nights — anything heavier and we feel the fit gets uncomfortable. One of our favorite midweights is most certainly the Minus33 Kancamagus Midweight Merino Wool Bottoms, which expertly weave together its 235 g/sm, 100% Merino wool with smooth, low profile flatlock seams, fitting our body almost perfectly. We reach for these bottoms when a cold front is forecasted to hit, having good thermoregulation in more frigid climes. The soft, smooth fabric is extra comfortable next to the skin and won't catch on your outer layers.

Just like other 100% Merino bottoms, give these a little more tender loving care — especially when all that's between you and indecency is your pair of Kancamagus. All Merino wool bottoms can be damaged by abrasive rocks, brush, or the like, and these are no exception. This pair is also just too warm for milder conditions, so it may be best to bring along a more appropriate pair in the summer. The REI Co-op Merino 185 Bottoms is an ecxellent choice for summertime when you still want an appreciable amount of warmth.

Read more: Minus33 Kancamagus Midweight Merino Wool Bottoms review

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

Our Favorite 3/4 Length


Smartwool Intraknit Thermal Merino 3/4 Bottom


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

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

What's not to like? If an almost compression level of tightness isn't your thing, you won't fall in love with the Intraknit Thermal as we have. The lack of a fly also dissuades some consumers from purchasing these bottoms. As does the price: the tech puts a heavy dent in the wallet. Also, Intraknit's polymath of fabrics makes them a little heavier than other pairs in our roundup. If ultimate warmth performance is of the utmost importance to you, then know there are better choices out there (and these are available in full-length, too), but we love these for many applications. However, if you prefer a snug-fitting layer over a compression tight, the REI Co-op Midweight Bottoms offer a comfortable four-way stretch at an extremely reasonable price.

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

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

Compare Products

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

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

Why Trust GearLab


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

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

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

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

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

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

Analysis and Test Results


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

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

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


What's the Best Value?


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

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

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

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

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

Warmth


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


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

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

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

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

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


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

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

Breathability


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


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

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

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

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

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

long underwear - the rei co-op lightweight bottoms feature very light -- and very...
The REI Co-op Lightweight Bottoms feature very light -- and very breathable -- perforated synthetic fabric.
Credit: Justin Simoni

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

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

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

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

Comfort and Fit


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


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

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

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

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

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

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

Durability


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


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

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

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

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

Drying Speed


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


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

But we're always surprised at how fast some of the heavier bottoms dry out. The Icebreaker Merino 200 Oasis Bottoms had excellent drying speed performance for their weight, as did the 3/4 length Ortovox 185 Rock'N'Wool Short Pant. Consolation prizes go to the Patagonia Capilene Midweight, our fastest synthetic dryer, as well as the Artilect Boulder 125 and Mons Royale Cascade Merino Flex Legging, which dried out quickly due to their overall svelteness on the scale.

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

Layering Ability


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


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

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

Conclusion


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

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

Justin Simoni and Aaron Rice