Reviews You Can Rely On

The 6 Best Long Underwear of 2023

We put men's long underwear to the test from brands like Smartwool, REI, Icebreaker, and others to find the best and warmest options on the market
Best Long Underwear of 2023
Credit: Justin Simoni
Friday December 2, 2022
Our Editors independently research, test, and rate the best products. We only make money if you purchase a product through our links, and we never accept free products from manufacturers. Learn more

Need new long underwear bottoms? We've been testing them for 9 years and showcase 12 of the current best options in this review. Our team of experts spent months, in every season, taking these layers on river trips, ski slopes, cold winter trail runs, long multi-pitch climbs, and multi-day backpacking trips. 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. We backed up our field research with objective, laboratory-style tests designed to analyze specific features and offer this comprehensive, unbiased review to help introduce you to your next pair of long johns.

We test both men's and women's versions of most apparel categories. Explore our in-depth testing by female reviewers in our women's specific long underwear review. Then, check out our writeup on the best base layer tops to see what to pair with the bottoms reviewed here. Finally, pick out some cozy hiking socks, and you'll be well on your way to adventure-ready.

Editor's Note: This review was updated on December 2, 2022, to test some new and updated models from Smartwool, REI, Ortovox, Icebreaker, and Meriwool.

Related: Best Long Underwear for Women

Top 12 Product Ratings

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Pros A nice balance of warmth and breathability, super cozy, nicely articulated designExtremely breathable, ultralight stretchy nylon/Merino wool blendTough synthetic fabric, four-way stretch for great range of motion, excellent performance for the priceShorter length reduces bunching near ankles, seamless panels provide additional articulation and ventilation only where needed, high waist and thick waistband keeps bottoms in placeEnhanced breathability in key areas, Merino wool blend is soft and warm for its weight
Cons Expensive, stretches out in between washes, slow to dry when saturatedPrice may make you do a double-take, care instructions need to be followed when dryingHeavier than wool bottoms for their warmthNo-fly design could be inconvenient underneath other layers, fit may be too tight for some body types, priceyBreathable mesh prone to ripping, expensive
Bottom Line Designed to keep you warm in the coldest conditions, this is a versatile pair of Merino wool bottomsA seriously tuned ultralight pair of wool/nylon blend leggings built for fast and light outdoor adventuresA great synthetic thermal long underwear at an unbeatable price for the warmth and durability they provideCarefully engineered 3/4 length thermals with compression pants-like tightness that’ll keep you warm and super comfortable while pursuing high output activitiesA technical performance base layer bottom for high output activities when you need both the warmth of wool and enhanced breathability in key areas
Rating Categories Smartwool Classic T... Artilect Boulder 125 REI Co-op Midweight... Smartwool Intraknit... Icebreaker BodyfitZ...
Warmth (25%)
9.0
5.0
7.0
7.0
7.0
Breathability (20%)
7.0
10.0
7.0
7.0
8.0
Comfort and Fit (20%)
8.0
8.0
7.0
7.0
7.0
Durability (15%)
7.0
6.0
9.0
8.0
4.0
Drying Speed (10%)
7.0
8.0
7.0
5.0
9.0
Layering Ability (10%)
7.0
8.0
7.0
9.0
9.0
Specs Smartwool Classic T... Artilect Boulder 125 REI Co-op Midweight... Smartwool Intraknit... Icebreaker BodyfitZ...
Material 100% Merino wool 85% Nuyarn Merino wool, 15% nylon 100% polyester 54% Merino wool, 43% polyester, 2% elastane, 1% polyamide Body: 97% Merino Wool, 3% Elastane,
Panels: 100% Merino Wool,
Eyelet: 98% Merino Wool, 1% Elastane, 1% Nylon
Fabric Weight 250 g/m² 125 g/m² Not stated ~200 g/m² ~150-200 g/m²
Weight (size medium) 8.3 oz 4.3 oz 7.4 oz 9.2 oz 6.9 oz
Insulation Weight Midweight Lightweight Midweight Lightweight Midweight
3/4 Boot-Cut Available? Yes Yes No Yes Yes
Fly? Yes No Yes No No
Dryer Safe? No No Yes No No


Best Overall Long Underwear for Men


Smartwool Classic Thermal Merino Bottom


77
OVERALL
SCORE
  • Warmth 9.0
  • Breathability 7.0
  • Comfort and Fit 8.0
  • Durability 7.0
  • Drying Speed 7.0
  • 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 bestowed upon 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 any 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.

Regardless of the thick construction of this pair of bottoms — and indeed, it is one of the most durable all-natural layers we tested — all Merino layers require a level of care that goes above and beyond most articles of clothing. The Classic Thermal tends to stretch out through regular use between washings, but don't be tempted to throw them in the dryer to shrink them back up. Careful laundering, and mainly flat or line air-drying, will help improve the longevity of this and all Merino base layers. While laundering may be an annoyance, the superb thermoregulation capability makes this pair of long underwear well worth the extra effort, especially for those working or playing in really cold conditions.

Read more: Smartwool Classic Thermal Merino Bottom review

best overall long underwear for men
The fabric of the Smartwool Classic Thermal Merino Bottom is soft and cozy, with a snug fit.
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 very much improved-upon four-way stretch 100% polyester fabric that we absolutely 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 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.

There are even fewer attributes of the Midweight Bottoms that we can really point to as weaknesses since they've been updated. They're a no-nonsense pair of gear that gets the job done well enough and isn't looking to collect accolades. For the price, the performance is really hard to beat. If you do need something that's warmer and maybe a little softer and comfier, it would be time to head on over to a wool option, and leave these for a milder day.

Read more: REI Co-op Midweight Bottoms review

long underwear - best synthetic bang for the buck
Worn underneath running tights, this midweight long underwear kept things toasty, despite the harsh wintry conditions.
Credit: Drew Crittenden

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 the temperatures really start to dip down.

Other than overall warmth and the value of getting a 100% Merino wool bottom at a steal of a price, there's little else that makes these bottoms stand out. But that's their charm: they're working behind the scenes (or underneath your pants) to ensure you're comfortable in the cold without needing any more fanfare. There may be a wash-in period to get the ultra-fine Merino wool to soften up a bit, so if you're first wearing of the Merino 250 Bottom is a bit itchy, give them a wash before bestowing your final judgment.

Read more: Meriwool Merino 250 Bottom review

long underwear - merino wool on a budget
The simple, no-nonsense construction of the Meriwool Merino 250 Bottoms still keeps a next to skin fit, helping with the natural wicking properties of Merino wool.
Credit: Justin Simoni

Best Lightweight Long Underwear


Artilect Boulder 125


74
OVERALL
SCORE
  • Warmth 5.0
  • Breathability 10.0
  • Comfort and Fit 8.0
  • Durability 6.0
  • Drying Speed 8.0
  • Layering Ability 8.0
Materials: 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

Tuned like a street-legal race car, the Artilect Boulder 125 leggings use advanced composite materials, like the comfy and 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 do look pretty darn good all on their own when you're lounging around your house or in the back of your van.

Just like 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 choose to pack along to make sure our next outdoor adventure is the coziest and lightest we can possibly have.

Read more: Artilect Boulder 125 review

best lightweight long underwear
These leggings worked admirably as a baselayer while bivvying right off the Colorado Trail or high up a mountain ridge during the Spring shoulder season.
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 lets more perspiration leave your body and 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 you don't prefer an almost compression level of tightness, you're not going to fall in love with the Intraknit Thermal as we have. A lack of a fly also turns off many to these bottoms. As does the price: the tech comes with a heavy hit to the wallet. The Intraknit's polymath of fabrics also makes these a little heavier than other pairs we've tested. If ultimate warmth performance is the most important trait you're looking for, there are better choices out there (and these are available in full-length, too), but we love these for many applications.

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

long underwear - our favorite 3/4 length
The Smartwool Intraknit Thermal Merino 3/4 Bottom layer well, integrating with other thick layers like a good warm wool sock.
Credit: Justin Simoni

Fast and Light in the Cold


Icebreaker BodyfitZone Merino 260 Zone Thermal Leggings


72
OVERALL
SCORE
  • Warmth 7.0
  • Breathability 8.0
  • Comfort and Fit 7.0
  • Durability 4.0
  • Drying Speed 9.0
  • Layering Ability 9.0
Materials: 98% Merino wool, 2% elastane | Weight: 6.9 oz (size Medium)
REASONS TO BUY
Ventilated panels provide a boost in breathability
Tight athletic fit integrates well with other performance layers
REASONS TO AVOID
Expensive even for a wool layer
Ventilated panels prone to tearing

A pair of long underwear made for the speed demons on the slopes? That's the Icebreaker BodyfitZone Merino 260 Zone Thermal Leggings. The secret sauce to their amazing warmth and breathability are super lightweight panels of wool fabric above the butt, crotch, and around the knees — areas where you want better breathability. At the same time, the rest of the legs — areas where you want to have more heat retention — are wrapped with heavier, plush Merino wool. The tight athletic fit aids in allowing perspiration to naturally wick off the body, leaving you feeling drier without bunching up under your tight-fitting outer layers. In our tests out in the backcountry, this works exemplary.

This design does have some drawbacks that we can't ignore. The very thin, almost 100% Merino wool panels are prone to ripping and tearing if you don't properly care for these leggings. Be gentle when washing and drying, and mindful when using them. Think of the BodyfitZone like any special, race-day equipment — like super lightweight carbon fiber ski poles, when your everyday pair are a more unpretentious aluminum. The price tag reflects this performance: these are some of the more expensive woolies out there, but for the right person and use cases, we definitley think they're worth it.

Read more: Icebreaker BodyfitZone Merino 260 Zone Thermal Leggings review

long underwear - the icebreaker bodyfitzone merino 260 make an excellent pair of...
The Icebreaker BodyfitZone Merino 260 make an excellent pair of leggings for fast and light missions in the high country.
Credit: Justin Simoni

Compare Products

select up to 5 products to compare
Score Product Price
77
Smartwool Classic Thermal Merino Bottom
smartwool classic thermal merino bottom long underwear review
$110
Editors' Choice Award
74
Artilect Boulder 125
artilect boulder 125 long underwear review
$110
Top Pick Award
73
REI Co-op Midweight Bottoms
rei co-op midweight bottoms long underwear review
$55
Best Buy Award
72
Smartwool Intraknit Thermal Merino 3/4 Bottom
smartwool intraknit thermal merino 3/4 bottom long underwear review
$115
Top Pick Award
72
Icebreaker BodyfitZone Merino 260 Zone Thermal Leggings
icebreaker bodyfitzone merino 260 zone thermal leggings long underwear review
$140
Top Pick Award
71
Patagonia Capilene Midweight Bottoms
patagonia capilene midweight bottoms long underwear
$79
70
Ortovox 185 Rock'N'Wool Short Pant
ortovox 185 rock'n'wool short pant long underwear
$100
69
Outdoor Research Alpine Onset Bottoms
outdoor research alpine onset bottoms long underwear
$89
68
Icebreaker Merino 200 Oasis Bottoms
icebreaker merino 200 oasis bottoms long underwear
$105
67
Meriwool Merino 250 Bottom
meriwool merino 250 bottom long underwear review
$60
Best Buy Award
63
Smartwool Classic All-Season Merino Bottom
smartwool classic all-season merino bottom long underwear
$85
60
REI Co-op Lightweight Bottoms
rei co-op lightweight bottoms long underwear
$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 You Should Trust Us


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.

Our testing of long underwear is divided across 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 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, exploring while out trail running, backpacking, alpine climbing, and ski touring. Aaron is joined by 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.

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.
Good for more than just snowy weather, long underwear bottoms are a...
Good for more than just snowy weather, long underwear bottoms are a versatile add to your wardrobe.

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. Obviously, for cold-weather activities like ice climbing and skiing, these are more of a necessity. But 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.


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 base 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 are 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 are 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 significant factors to consider when shopping for long underwear. A layer's ability to keep you warm is rooted in its ability to wick sweat away from your body, keeping you dry and comfortable while active. So while we often notice a correlation between warmth and the thickness of a material, we also have to take into account the type of fabric and fit.


Base layer bottoms are versatile, but warmth is a dynamic metric because 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 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. Do you want versatility across all four seasons or just mid-winter warmth? Are you layering them under a single, technical hardshell pair of 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 the most practical.

long underwear - a snug fit makes the 100% merino wool meriwool bottoms perfect for...
A snug fit makes the 100% Merino wool Meriwool bottoms perfect for layering up in the cold.
Credit: Justin Simoni

If you need bottoms for activities in the bitter cold, we recommend the Smartwool Classic Thermal Merino or the Meriwool Merino 250 based on overall warmth. 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 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 Icebreaker BodyfitZone Merino 260 and Artilect Boulder 125 rely upon moisture-wicking capability more than warmth by insulation all alone.

long underwear - a good pair of long underwear will keep you warm enough while...
A good pair of long underwear will keep you warm enough while cooking so that you don't have to huddle around the campfire.
Credit: Aaron RIce

Breathability


Breathability is a quality that can make or break how effective a base layer is when it comes to regulating your 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 continuously dry out 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. The most breathable layers we tested, not so shockingly, are on the lighter side in terms of fabric weight.

long underwear - there&#039;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. 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.

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

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 Icebreaker BodyfitZone Merino 260 uses a different approach, opting to use almost pure Merino wool with a little elastane added in and lightweight panels of wool in strategic places to allow perspiration to escape while keeping the rest of your legs cozy. 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 - breathability was excellent while on the go with the artilect.
Breathability was excellent while on the go with the Artilect.
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

long underwear - a snug fit and minimal seams make the icebreaker bodyfitzone layer...
A snug fit and minimal seams make the Icebreaker BodyfitZone layer well, especially with other tight fitting layers. The back panel is thinner, to increase breathability in a high perspiration area.
Credit: Maddock Rigby

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. Many bottoms mix synthetic fibers with their wool to add long-lasting stretch to hug the body. Find this material in the uber comfy Smartwool Intraknit and Artilect Boulder 125.

long underwear - seamless paneling on the knees of the intraknit are made of a more...
Seamless paneling on the knees of the Intraknit are made of a more flexible fabric, helping with articulation. The 3/4 length ends at about the same place a crew-length sock will meet up.
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 are a polyester-wool blend that also tease 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 all-natural options are improving, the most durable pairs of long underwear we tested are still synthetic. The REI Co-op Midweight 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 when you consider the thinner fabric utilized.

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, 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. The Icebreaker BodyfitZone Merino also dry out quickly, helped by the very thin layers of wool panels used in places where exceptional wicking and ventilation are wanted. Consolation prizes go to the Patagonia Capilene Midweight, our fastest synthetic dryer, and the Artilect Boulder 125, which dried out quickly due to its 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.


We gave high marks in layering ability to the Icebreaker BodyfitZone for having a very snug fit as well as for having excellent breathability for an almost 100% Merino wool layer. The Smartwool Intraknit Thermal features an even tighter, 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 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. To find your next perfect pair, it is important to consider your temperature disposition, as well as how and when you plan to use them. 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

Aaron Rice and Justin Simoni


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