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Need new long underwear bottoms? We've been testing them for 7 years and showcase 11 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 pair you with your next pair of long johns.
Materials: 100% Merino wool | Weight: 6.4 oz (size Medium)
REASONS TO BUY
Warm for weight
Attention to details of fit
REASONS TO AVOID
Heavier than fabric weight suggests
Slow to dry
Merino wool is not dryer-friendly
After months of testing, the Ortovox 185 Rock'N'Wool Pant has risen through the ranks to land on top of the pile of best long underwear bottoms. These bottoms hit that Goldilocks zone of base layer weight — not too light, but not too heavy. They offer the type of fit and comfort that will have you wearing them long after the day's activities come to an end. The 100% Merino wool knit is nearly unmatched regarding next-to-skin comfort. Most notably, the wide waistband is thoughtfully sewn on the outside of the pant, eliminating any chance of that annoying itch that often develops after these all-natural layers inevitably stretch out.
The weight-to-warmth ratio of these bottoms is fantastic — featuring a level of warmth that far exceeds their fabric weight — but this does come at some expense of breathability. Slide this pair of long underwear on before a long day of ski-touring, and know that the Merino wool will efficiently wick away any sweat on the way up. They will keep you dry, comfortable, and warm standing on the summit but will not be as breathable as a lighter-weight pair. The wool knit is uncharacteristically durable, but like all 100% Merino layers, these are no doubt more prone to snags and tears than a full synthetic model. The 185 Rock'N'Wool Pant is also an investment, but with proper care, these will likely provide years of winter-time adventure.
Materials: 100% polyester | Weight: 7.7 oz (size Medium)
REASONS TO BUY
Warm as well as breathable
Very comfortable synthetic
REASONS TO AVOID
Slightly short inseam
Stretchier fabric could make these even better
The apple doesn't fall far from the tree, and like its lightweight brethren, the REI Co-op Midweight Bottoms are a value-packed, durable, and straightforward pair of long underwear. You'll certainly want to favor these for colder missions in winter-like conditions and/or if you run particularly cold: the added thickness of the fabric brings with it additional warmth retention. We were impressed by the wicking qualities of the soft, brushed interior, which trapped our body heat while transporting moisture toward the surface. We also appreciate the smooth, silky hand of the exterior side of the same dual-textured fabric, which did a lot to keep them looking brand new. As far as fully-synthetics go, this is one of our favorites, especially when looking at the price.
There's not much we didn't like about the Midweight Bottoms, but if the weather is warm enough, these may also prove to be too warm. It's hard to match wool's absolute comfort or breathability properties, but these come closer than most other synthetics. If wool doesn't work for you, these are a righteous pair, especially for the price.
Setting the standard for a simple, no-nonsense pair of long underwear, the REI Co-op Lightweight Bottoms are everything you need to help extend your playtime into the colder months. Offering quality performance at a price point much lower than most models in this review, these bottoms continue to define value in this category. The lightweight polyester knit features a bit of spandex for a little extra stretch, adding mobility to these form-fitting bottoms. As a lightweight option dappled with small vents, this highly breathable layer easily doubles as a pair of cool-season running leggings.
These bottoms have a shorter inseam, but REI offers a longer option that may better suit taller folks. And while we wished the full-synthetic build offered a bit more durability, our abrasion test far exceeds most real-world applications. We don't suggest it, but even if you were to ruin these bottoms dragging them up sandstone towers on your next desert climbing escapade, at least you didn't drop a huge wad of cash on them. Great for chilly nights on late summer camping trips and your more aerobic winter activities, this versatile pair of johns satisfies a lot of needs for little cash.
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.
Materials: 100% Merino wool | Weight: 7.6 oz (size Medium)
REASONS TO BUY
Cozy and comfortable
Merino wool-lined waistband
REASONS TO AVOID
Stretches out between washings
It should not be surprising that we also love the Smartwool Merino 250 Bottoms. This pair's combined warmth and comfort earn our nod when the temps really dip. The special interlock knit of this design provides exceptional breathability, especially considering the thick, 250 g/m² cut of the 100% Merino wool. Updates include rear gussets to match the front, improving upon issues we've had with the fit in the past. The extra-wide, wool-lined waistband and full-flatlock seam support 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 Merino 250 Bottoms tend 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.
We start our review process with research into what's out there. After sorting through the market and making our selection, we purchase our test fleet at full price. Our experts then develop a series of tests to help assess and judge each model on warmth and breathability and other more targeted laboratory tests to judge fit and durability features. From the alpine peaks of the Rocky Mountains and the Pacific Northwest, back down to the high deserts of the US Southwest, we put these bottoms to the test through a variety of activities. We wore them climbing, trail running, backpacking, and uphill and downhill skiing, and continually assessed and re-analyzed their relative strengths and weaknesses throughout our adventures.
Our long underwear testing is divided across four different metrics:
Warmth (30% of overall score weighting)
Breathability (30% weighting)
Comfort and Fit (30% weighting)
Durability (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. Outdoor educator and guide Roland Mott also contributed to this review, bringing the experience and attention to detail that only comes from a life avidly spent engaged in a variety of outdoor activities (often spent wearing long underwear). Roland earned a degree in Outdoor Recreation Leadership in 2010 and has guided rivers, backpacking, and climbing for 12 years throughout the US and Central America. Rounding out the impressive test team is Justin Simoni. Simoni is 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 been working closely with outdoor gear companies for over a decade, bringing his experience and expertise to the table.
Analysis and Test Results
Long underwear (also commonly referred to as base layer bottoms) is important in keeping you warm and regulating 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.
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.
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.
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 that their longevity adds to their value.
The REI Co-op Lightweight Bottoms may not provide the right amount of warmth for long adventures in snowy conditions, but they're versatile enough to both walk the dog on cold winter days and to pack as a lightweight extra layer on a backpacking trip. For those needing a warmer pair of bottoms at a great price, consider the REI Co-op Midweight Bottoms. For the sustainably-minded, the Patagonia Capilene Midweight Bottoms are a synthetic option made from 100% recycled polyester. Finally, in terms of balancing price and warmth, the Smartwool Merino 150 Bottoms are the most reasonably priced 100% Merino wool option in our review.
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 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, fall backpacking, and sleeping in the back of the 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.
If you need bottoms for activities in the bitter cold, we recommend the Smartwool Merino 250, Ortovox 185 Rock'N'Wool, or Arc'teryx Rho LT Bottoms, based on overall warmth. If you're looking for a more versatile pair of long underwear, the Smartwool Merino 150, REI Co-op Midweight Bottoms, and Icebreaker Merino 200 Oasis Bottoms are midweight options that tend to blend the seasons. If warmth isn't as pressing for you, a lightweight option like the REI Co-op Lightweight or Carhartt Base Force bottoms 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 Outdoor Research Alpine Onset Bottoms and Artilect Boulder 125 Leggings rely upon moisture-wicking capability more than warmth by insulation alone.
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 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.
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 well 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 Merino 150 and Icebreaker Merino 200 Oasis bottoms 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 Lightweight bottoms are both full synthetics that do a solid job of wicking away moisture.
That said, the two front-runners in our testing are the Outdoor Research Alpine Onset and Artilect Boulder 125. The Alpine Onset is a hybrid of recycled polyester, Merino wool, and elastane jersey, which combines the best of each fabric to provide top-notch breathability. The Artilect Boulder 125 leggings use an 85% Merino wool and 15% nylon blend to produce a thin 125 g/m² fabric that's super breathable while staying durable.
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 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. Particularly comfortable are the 100% Merino bottoms and models made with recycled polyester, like the Patagonia Capilene Midweight. So when it comes to ranking pairs of long underwear side-by-side, it is the fit that sets them apart. If you are looking for that ultra-soft pair, perfect for getting after it or for just hanging out and relaxing, check out the Smartwool Merino 250 and Arc'teryx Rho LT bottoms. For options that are still going to feel like your favorite pair of sweatpants, just with a little more cut, look to the Ortovox 185 Rock'N'Wool or Smartwool 150. If you're looking to fit in with the yoga or fall-running crowds, consider the Icebreaker Merino 200 Oasis, and for second-skin comfort, look no further than the sheer Artilect Boulder 125.
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 has been historically susceptible to rips, tears, and punctures, but brands have been making 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 Merino 150 and 250 bottoms particularly durable. The Artilect Boulder 125 does the same thing.
Washing and drying in a machine is the quickest path to destruction for long underwear, particularly for fully Merino wool garments. A tip for washing Merino layers: washing them in a mesh bag significantly reduces the wear they experience by bouncing around during wash cycles. Additionally, as with most wool layers, we fully endorse the manufacturer's suggestion of laying the long underwear flat to dry.
Other designers opt to blend polyester fibers with Merino wool to increase product life, like the Outdoor Research Alpine Onset. While synthetic fibers are traditionally more durable, the thinner, lightweight bottoms are the most susceptible to damage, regardless of fabric material. However, the Carhartt Base Force Lightweight bottoms break this generalization, easily standing up to our overly aggressive abrasion test.
While all-natural options are improving, the most durable pairs of long underwear we tested are still synthetic bottoms. Thanks to a brushed-nylon face fabric, the Arc'teryx Rho LT showed very little wear after both laboratory and extensive field testing. For a more budget-friendly option, consider the REI Co-op Midweight Bottoms, which scored extremely well in durability. Of the Merino wool layers, the thick fabric of the Smartwool Merino 250 is the most durable, and the slightly thinner Ortovox 185 Rock'N'Wool Pants prove themself worthy with similar durability results.
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 land on 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.
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GearLab is founded on the principle of honest, objective, reviews. Our experts test thousands of products each year using thoughtful test plans that bring out key performance differences between competing products. And, to assure complete independence, we buy all the products we test ourselves. No cherry-picked units sent by manufacturers. No sponsored content. No ads. Just real, honest, side-by-side testing and comparison.