The 8 Best Long Underwear for Men

Best Synthetic Long Underwear for Men

Arc'teryx Rho Heavyweight Bottoms

Materials: 53% polyester, 38% nylon, 9% elastane | Weight: 9.5 oz (size Medium)

When you're looking for one of the warmest synthetic long underwear bottoms made, reach for the Arc'teryx Rho Heavyweight. These thick, long johns wear like tight joggers, locking in warmth all through your lower half. If wool fibers don't agree with your skin, these make a great alternative. “These are the long bottoms to grab when you want serious warmth retention in your layering strategy,” notes our main reviewer. A far more sheer outer face complements the fuzzy nap underside of the fabric, trapping heat next to your skin while your top layers easily lay against the Rhos without snagging.

The Arc'teryx Rho Heavyweight Bottoms are excellent mid-heavyweight bottoms, ideal for cold days when warmth is a top priority. But they are not the bottoms for transitional seasons or high-intensity activity. Our tester confirms, “A poor matchup would be to don these on a brisk day for a fast run: you'll quickly overheat, and sweat will start to build up, making them stinky and uncomfortable.” But they will serve well when temperatures drop, and you need to bring the heat. They also come at a high price tag, which means that they won't appeal to everyone. A more adaptable pair of long underwear for cooler conditions is the REI Co-op Midweight Bottoms, which are lighter and far cheaper. Being so thick also means the Rho Heavyweights wear a little heavier than almost every other pair we tested in our lineup. And if you already plan to work up a sweat, such ultra-warm bottoms may not be breathable enough to keep up. The Patagonia Capilene Midweight Bottoms is a much more breathable pair that's excellent for high-output activities.

Read more: Arc'teryx Rho Heavyweight Bottoms review

Best Overall Long Underwear for Men

Smartwool Classic Thermal Merino Bottom

Materials: 100% Merino wool | Weight: 8.3 oz (size Medium)

We adore the Smartwool Classic Thermal Merino Bottom and have given it our top honors. The combined warmth and comfort of these long johns 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. Our lead reviewer sang the praises of this design: “The gusseted crotch is a big win for me as I'm riding my bike all year 'round, and getting the seams out of the way is just way more comfortable.” 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. “These pants are plush and my ideal companion for full days spent outside through the coldest months of winter,” our lead reviewer adds.

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 SmartWool Classic Thermal Merino 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 Arc'teryx Rho Heavyweight Bottoms or REI Co-op Midweight Bottoms may suit you better. They'll last much longer when thrown in the dryer if you desperately need them immediately or if they sneak in by accident. When you put the Classic Thermals away for the season, look into grabbing the Smartwool Classic All-Season Merino Bottom for the rest of the year. What we love about the design of the SmartWool Thermals can also be found in these long bottoms, except the fabric is lighter weight, which is perfect for shoulder season and cold summer nights up high.

Read more: Smartwool Classic Thermal Merino Bottom review

Best Synthetic Bang for the Buck

REI Co-op Midweight Bottoms

Materials: 92% recycled polyester, 8% spandex | Weight: 7.4 oz (size Medium)

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 poly-spandex 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. “The REI Midweights are one of the burliest pairs I've tested, thanks to their heavier synthetic fabric and tight weave,” reports our lead reviewer. It's the warmest synthetic mid-layer we've tested, giving even some 200 g/m² thick 100% Merino wool thermal underwear a run for their money. Notably, during field testing, these delivered even on high peaks in heavy winter conditions — the ultimate test of warmth, when performance really matters.

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. Their performance is tough to beat, considering the price. But If you're in the market for an even warmer layer (and maybe a softer and comfier one), it could be time to reach for a wool option like the Smartwool Classic Thermal Merino Bottom and leave midweights like these for a milder day. If you want to stick with synthetics, one of the only warmer pairs you'll find is the Arc'teryx Rho Heavyweight Bottoms, whose fleece-lined inner face is on another level of warmth, likely the warmest synthetic long underwear in our lineup and matching — or even bettering — the toastiest Merino wool bottoms we've tested.

Read more: REI Co-op Midweight Bottoms review

Our Favorite Merino Wool on a Budget

Merino.tech Bottoms

Materials: 100% Merino wool | Weight: 7.8 oz (size Medium)

We're always on the lookout for quality products found at a good value. The Merino Tech Bottoms impressed us by delivering a pair of soft, comfortable, and super warm thermal underwear at a price we can justify — even when on a budget. “If you're looking to grab your first pair of wooly bottoms, I would not hesitate to recommend these as a solid choice,” notes our lead reviewer. The key is the fabric's super finely spun 100% Merino wool and thoughtful construction using low profile, strong flatlock seams. The next-to-skin fit will move with you while you're skinning up a mountain and wick moisture away from the body as you sweat.

For all its admirable qualities, the material choice is also one of the biggest weaknesses of the Merino Tech Bottoms. Wool is a more delicate fabric, so to preserve the lifespan of your leggings, it will be important to layer them under a more protective outer pant to avoid tearing against abrasive surfaces. You should also treat such fabric with tender, loving care when washing and drying. Although Merino.tech states these are dryer-safe, our test team has reservations and would still suggest drying these on the line or laying them flat to dry. Other entry-level options exist in our lineup, especially if your budget is really tight. Synthetic or cotton-synthetic blends like the Amazon Essentials Set and WEERTI Thermal Fleece Lined Set fall into this category. Still, neither will be as warm, breathable, or activity-ready as the Merino.tech. The Merino Tech Bottom makes a good pair of long bottoms for cold, active days: ski touring, snowshoeing, or a very cold run. If you need warmth, another excellent Merino wool choice similar to the Merino Tech Bottoms is the Meriwool Merino 250 Bottom, which can be found at a similar price and offers comparable performance.

Read more: Merino Tech Bottoms review

Best Lightweight Long Underwear

Artilect Boulder 125

Materials: Nuyarn (85% Merino wool, 15% nylon) | Weight: 4.3 oz (size Medium)

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. The eyelets act almost like the pores on your skin, allowing perspiration to easily exit from the skin and fabric into the air. All this will keep you perfectly thermoregulated on your next light and fast mission through chilly conditions. And even though you'll most likely wear these under 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 their speed-over-everything philosophy, the Boulder 125 isn't meant to be an all-rounder. Wear them when the weather is fairly mild, and swap them out for something more substantial on those colder winter missions. “The Artilects just don't have enough weight to be useful in the colder, darker months, ” reports lead tester Justin Simoni. When temps drop deep, check out the Mons Royale Cascade Merino Flex Legging, which will wear a little warmer, but don't tip the scales all that much more using 180 g/sm fabric rather than 125 g/sm of the Boulder 125's. The Mons Royal also adds a fair bit of spandex to their wool-nylon blend, adding stretch to strengthen the wool where it is most delicate. The 150 g/sm Smartwool Classic All-Season Merino Bottom also utilizes wool fabric with a nylon core, but their fit isn't quite as slim as the Boulder 125s. These are really technical long bottoms, and the price for such a luxe pair of long underwear is predictably higher than other options. Yet with the Artilect Boulder 125, you get what you pay for. If durability concerns you, try out the Patagonia Capilene Midweight Bottoms instead, as they side-step the wool's problem of low abrasion resistance with a fully synthetic design that comes in at a lower price.

For colder conditions, reach for the Smartwool Classic Thermal Merino Bottom instead.

Read more: Artilect Boulder 125 review

Best Midweight Long Underwear for Men

Minus33 Kancamagus Midweight Merino Wool Bottoms

Materials: 100% Merino wool | Weight: 8.9 oz (size Medium)

Midweights are our favorite for cold days and nights. If you are looking for a pair of long underwear to help keep you warm in wintry conditions above all else, the Minus33 Kancamagus Midweight Merino Wool Bottoms is a pair you should seriously consider. One of our favorite midweights, these are expertly structured, featuring 235 g/sm, 100% Merino wool with smooth, low-profile flatlock seams to fit the body almost perfectly. Our lead tester notes, “I wouldn't suggest wearing too thick of thermal underwear in all but the most extreme conditions, but these are a great choice when you know a storm is brewing.” We reach for these bottoms when a cold front is forecasted to hit, as we found they provide good thermoregulation in more frigid climes. Plus, the soft, smooth fabric is extra comfortable next to the skin and won't catch on your outer layers.

Like other 100% Merino bottoms, the Minus33 Kancamagus Midweights require a little more tender loving care, especially when they are all between you and a moment of backcountry exposure. Washing and drying can be the time when damage happens. As with any wool, consider washing them sparingly. They won't hold onto odor like other materials and can be worn many times before genuinely needing a good wash. All Merino wool bottoms can be damaged by abrasive rocks, brush, or the like, and these are no exception. The Kancamagus leggings are also just too warm for milder conditions, so bringing along a more appropriately light pair in the summer may be best. The REI Co-op Merino 185 Bottoms is an excellent choice for summertime when you still want an appreciable amount of warmth, as their 185 g/sm weight makes for a better all-rounder. If the Kancamagus is too delicate and expensive for your blood, look at a synthetic pair, like the REI Midweight Bottoms, that can take far more abuse.

Read more: Minus33 Kancamagus Midweight Merino Wool Bottoms review

Our Favorite 3/4 Length

Smartwool Intraknit Thermal Merino 3/4 Bottom

Materials: 54% Merino wool, 43% polyester, 2% elastane, 1% polyamide | Weight: 9.2 oz (size Medium)

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 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. If you prefer to be hugged tightly by your thermal bottom as you move, these are for you.

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 Merino 3/4 Bottoms as we have. Look at the Minus33 Kancamagus Midweight Merino Wool Bottoms for a pair of high-quality wool bottoms with a looser fit. The lack of a fly in the Intraknit Thermal 3/4s may also dissuade some consumers from purchasing these bottoms. “I prefer no-fly myself, but if easy access under multiple layers is a requirement, that will be a dealbreaker,” shares Justin Simoni, our lead reviewer. The Ortovox 185 Rock'N'Wool Short Pant is another 3/4 length option that coincidentally comes without a fly. You will find a fly in the similarly weighted REI Co-op Merino 185 Bottomsif it matters. Intraknit tech does put a heavy dent in the wallet, and their polymath fabrics make this pair a little heavier than other options in our review. If ultimate warmth performance is of the utmost importance to you, there are better choices (available in full-length form), but we love these 3/4 leggings for many applications. If you prefer a snug-fitting layer versus 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

Excellent Value for Cold Winter Days

Meriwool Merino 250 Bottom

Materials: 100% Merino Wool | Weight: 7.9 oz (size Medium)

Making 100% Merino Wool apparel approachable for the masses is the Meriwool Merino 250 Bottom. We appreciate these affordable leggings' no-nonsense construction and super plush, cozy, 100% Merino wool fabric. 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. A wide range of sizes is available to accommodate a broad range of shoppers' needs, which is something of particular note since not everyone looking to stay warm is also a super-athlete. It's great that Meriwool offers the Merino 250s in many sizes.

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. If you need a lot of features or a more technical performance out of your long under, you will want something like the Smartwool Intraknit Thermal Merino 3/4 Bottom. But that's the Meriwool's charm: they're working behind the scenes (or underneath your pants) to ensure you stay comfortable in the cold without needing a bunch of 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 to be somewhat itchy when you first wear them, be sure you wash them before bestowing your final judgment. If you'd rather go with a comfier option, we like the feel of the Smartwool Classic All-Season Merino Bottom, which blends wool and stretchy nylon. If money is no object, for pure comfort in casual settings, you can't beat the synthetic Arc'teryx Rho Heavyweight Bottoms.

Read more: Meriwool Merino 250 Bottom review

Compare Products

Compare select up to 5 products to compare

	Score	Product	Price
	81	Arc'teryx Rho Heavyweight Bottoms Best Synthetic Long Underwear for Men	$120
	76	Smartwool Classic Thermal Merino Bottom Best Overall Long Underwear for Men	$115
	74	Artilect Boulder 125 Best Lightweight Long Underwear	$120
	73	REI Co-op Midweight Bottoms Best Synthetic Bang for the Buck	$55
	73	Minus33 Kancamagus Midweight Merino Wool Bottoms Best Midweight Long Underwear for Men	$80
	72	Smartwool Intraknit Thermal Merino 3/4 Bottom Our Favorite 3/4 Length	$120
	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 Excellent Value for Cold Winter Days	$60
	67	REI Co-op Merino 185 Bottoms	$80
	67	Icebreaker Merino 200 Oasis Bottoms	$105
	66	Merino.tech Bottoms Our Favorite Merino Wool on a Budget	$59
	64	Smartwool Classic All-Season Merino Bottom	$90
	62	WEERTI Thermal Fleece Lined Set	$30
	60	Thermajohn Thermal Fleece Lined Set	$40
	56	Amazon Essentials Set	$21

Why Trust GearLab

We take a two-pronged approach while testing men's long underwear. One side involves a lab setting where we performed specific, repeatable tests to compare each bottom with the others in the lineup directly. Metrics like durability involve our harsh abrasion test and repeated washing and drying. Warmth and breathability tests are done in climate-controlled rooms to compare all bottoms in a more standard and equal setting. The second leg of our testing journey involves taking these bottoms with us on our favorite outdoor pursuits and examining 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 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 equipment 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.

Analysis and Test Results

Long underwear (commonly called base layer bottoms or thermal underwear) 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 become necessary when tackling cold-weather activities like ice climbing and skiing. Regardless of the situation, these bottoms keep you dry and comfortable by wicking sweat away from your body, improving thermoregulation and your outdoor experiences.

We design our field and laboratory testing to be 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 working or 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.

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 and Merino Tech Bottom buck the trend of wool being super expensive and are great introductory pairs to the world of wool.

Warmth

Warmth is one of the most important factors 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 often correlate to a warmer base layer, but the fabric type and fit can also impact how breathable and comfortable the thermal 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, 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.

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 a thick pair of ski pants that already offer a degree of warmth and insulation? It is important to know that the warmest bottoms aren't always the most practical.

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 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, the Meriwool Merino 250, and the Merino Tech Bottoms are all excellent choices.

Need winter-level warmth but don't want to go the wool route? Your options may be limited, but the Arc'teryx Rho Heavyweight Bottoms are an excellent synthetic choice with a heavily insulating yet soft next-to-skin interior and an outer layer that's sheerer and won't catch on your exterior pants layered above.

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 lets your bottoms dry out continuously, even when you're sweating. 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 on our top half. But it does house some of our major working muscles and thus is an area 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 lighter in terms of their fabric weight.

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 is a full synthetic bottom that does 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.

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.

The Mons Royale Cascade Merino Flex Legging also scores admirably in this metric. The Merino-blended fabric seems thinner than its advertised 180 g/m², resulting in a lighter-weight pair of bottoms than we expected. They also have an athletic fit, hugging tightly around your legs, which helps transfer moisture away from your skin.

Cotton-based long underwear doesn't score too strongly compared to far more expensive wool, nor does it compare well with many synthetics when wet. Still, if kept relatively dry, the Amazon Essentials Set showed good results using our air permeability tests.

Comfort and Fit

Comfort is a reasonably uniform metric 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 subjective, as “perfection” 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 that said, we always suggest trying clothing on in person so you can decide 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

We only test high-quality products here, so comfort is fairly uniform. But 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 their lighter weight brethren, the Classic All-Season.

Many bottoms mix synthetic fibers with wool to add a long-lasting stretch that hugs the body. This material is found 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 band's pressure around a wide area.

It's hard to argue against a pair of long bottoms that feel like luxurious, insulated leggings, but in a sense, that's what the synthetic Arc'teryx Rho Heavyweight Bottoms are. If you're not hitting the slopes with these under your ski pants, they're just as excellent lounging around the hotel sipping on cocoa.

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 teases both materials' benefits into one.

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 their 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.

Drying Speed

We test and report on drying speed for a few important reasons. First and foremost, many 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 in addition to shedding 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 indicate 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. 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 from. We did notice the start of some pilling in both of these, so it is best to dry these out on the line rather than in the dryer.

We were surprised at how fast some heavier bottoms in our test group dried 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 Arc'teryx Rho Heavyweight Bottoms dazzled us with how fast they dried, especially compared to the midweight woolen options that occupy the same cold weather niche. 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.

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 various 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 prevent 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.

How to Choose a Men's Long Underwear

When temps start to dip down, it's time to think about getting a pair of long underwear to supplement the warmth your outer layers may provide. But choosing just the right pair may seem daunting, with so many options now available.

Does the type of fabric make a difference?

One of the biggest differences across long underwear options is the type of fabric they're made out of. Almost all the long underwear in our lineup are either made of wool, a wool blend, polyester, or a cotton blend. Each has its advantages.

Wool

Wool is soft, feels great in hand, and has exceptional insulating properties and breathability. It even performs well when wet, staying warmer than other fabric types. Although an exceptional material, it can also be the most delicate, both while wearing and washing. It can also be one of the most expensive.

Wool blends attempt to improve many shortcomings associated with 100% wool fabrics. Polyester is usually added to the wool fiber to enhance its strength and even to provide a little more stretch to the fabric. Blends can add more value to your pair of long underwear but don't necessarily help with the cost.

Polyester

Polyester pairs can have a huge “leg up” to their wool counterparts when it comes to durability, as a polyester fabric can be knitted with a strength that far exceeds that of wool at the same weight. You'll give up a little in absolute warmth and perhaps comfort, but usually, the price of a polyester bottom makes them very attractive, especially in the mid and lightweight subcategories, where a wool pair may prove too delicate to wear for most.

Cotton Blends

Although less appropriate for outdoor activities, cotton-blended fabrics make cozy options perfect for lounging around and tackling low-output activities like dog walks on winter days, and they're usually priced as a budget item with a performance to match. These will do the job if you need just a simple pair of long bottoms for more casual use. But they are not advisable for outdoor pursuits given how highly absorptive cotton can become, leaving you wet, cold, and miserable — a dangerous combination when exposed to the elements. If you are heading up Denali mid-winter or skiing amid the Rockies on a spring day, skip the cotton and pick up something in wool or synthetic that is sure to be moisture-wicking and quick drying.

What Are The Insulation Weight Classes About?

Generally, long underwear can be categorized by weight: “lightweight,” "midweight," “heavyweight,” etc. The heavier the weight of the fabric, the more insulation the bottoms have. If you're going to be in bitterly cold conditions, you'll want to pick out a pair of long underwear that's on the heavier side of things. But if you're just looking for a pair to wear while sleeping out on a backpacking trip during the summer, you probably want to try a lighter-weight pair.

Heavier long underwear may be warmer, but you'll also find them less breathable, and typically, they will take longer to dry out. So, if you start your morning run wearing a heavy pair of long underwear, chances are you'll sweat through them before you finish your run, negating the insulative qualities of the underwear. It may be better to start with a lighter weight but more breathable pair of leggings, which may not be warmer but will more easily breathe and wick away sweat, leaving you as comfortable at mile 10 as you wear at mile 1.

How Much Should I Spend on Long Underwear?

The best long underwear to buy isn't always the most expensive, but you want to ensure what you buy fits the purpose you're looking to fill. The least expensive pairs in our review are cotton blends that may be perfect if you only want something extra to wear at home when the temperature dips lower than usual for a few weeks. But if you regularly recreate outside, you may want to spring for a more performative pair of long underwear that wicks away moisture and breathes well while keeping you extra warm. If you're traveling in the backcountry, don't underdress to save a few dollars and then need to call Search and Rescue!

Some of the most expensive pairs in our lineup are made of wool and wool blends, as wool is an expensive material. Yet it offers excellent performance, especially when assessed for the warmth it provides. Polyester fills an excellent middle ground, being a good choice for all but extreme conditions. You might consider using a polyester bottom when absolute performance isn't necessary. Cotton blends, as we've noted, are for more casual uses only and are not a safe bet to keep you warm on outdoor adventures. But they can be a good choice if budgets are very tight and you need something for around town — just understand that they come with very real safety limitations.

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 and 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 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 will keep you warm and dry no matter the activity or occasion.