Seeking the best long underwear bottoms? After researching 30+ different models, we bought and tested 9 of the best options for several months. Testing each pair was indeed an adventure, taking our well-seasoned experts on gnarly river trips, cold winter trail runs, and up long multi-pitch climbs to beautiful summits. Different climates were sought out as we exposed ourselves to everything from cold, wind-blown ridges to warm desert weather. After becoming very acquainted with each on the trail, we took them to the lab to objectively measure drying speed and durability. This comprehensive review sums up our experience and offers a trustworthy and unbiased review to help you find your next 'next to skin' compadre.
The Best Long Underwear Bottoms
Best Overall Long Underwear
Ortovox Rock'N'Wool Pant
A newcomer to this stage, quickly garnering crowd favor, the Ortovox Rock'N'Wool Pant rose through the ranks to land on top. These bottoms hit that Goldilocks zone of base layer weight — not too light, but not too heavy — and bring along comfort and a fit that will keep you wearing them long after the day's activities come to an end. The 100% Merino wool knit is unbeatable in terms of plush, next-to-skin comfort, and these bottoms sport an equally soft waistband that 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, to carry you through the coldest months of winter. 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, keeping you dry, comfortable, and warm standing on the summit. The wool knit is uncharacteristically durable, and even sports knee-pads to show off its resistance to abrasion. A simple design, with minimal articulation, features a fit that is somehow both relaxed and athletically cut — this pair of long underwear is just as comfortable out on the hill as they are hanging around the house. No pair we tested balanced the key performance characteristics of base layer bottoms better than these. An investment, but with proper care, we see these affording years of winter-time adventure.
Read review: Ortovox Rock'N'Wool Pant
Best Bang for the Buck
REI Co-op Lightweight Bottoms
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 any other base layer in this review, these bottoms continue to define our Best Buy Award in this category. One of our biggest concerns with these bottoms is the shortcut of the legs, but REI offers a longer option that may better suit even those with not-so-long legs. 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 escapade, at least you didn't drop a hundo on them.
The lightweight, majority polyester knit has been upgraded this season with a bit of spandex, offering a little extra stretch and 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. Great for the chilly nights of summer camping trips and for your more aerobic winter activities, this versatile pair of johns is ready for any adventure you can dream up — just as long as it doesn't involve standing for extended periods in the frigid cold.
Read review: REI Co-op Lightweight Bottoms
Best for Warmth
SmartWool Merino 250 Bottoms
We've tested the top and the bottom of the SmartWool Merino 250, and we love the fabric! The warmth and comfort of the thick, cush 250 g/m², 100% merino wool are unparalleled. These bottoms balance extreme warmth and breathability with a grace that is worthy of praise. Built for the coldest conditions, but efficiently wicking away sweat, these breathe so well that they perform nearly just as beautifully when the temperature warms up a bit. Flatlock seams and a wide, merino-wrapped waistband offer all-day comfort. With the added bonus of merino wool's natural anti-odor capability, you don't have to worry about making a stink after a long, hard day in the hills.
This is the thickest merino fabric that we tested, which makes it one of the most durable merino layers in our review, but it still is not bulletproof and requires a level of care that goes beyond most pieces of gear. We don't love the fact that these bottoms tend to stretch out after regular use. The fabric will recover from its stretch after a wash, but the double-edged sword is that they will last longer with fewer washes. Although the comfort is heavenly, the fit could use some fine-tuning, especially the crotch — the infamous long underwear crotch-sag still lives on in these bottoms. Able to provide comfort and performance in a wide range of temperatures, these bottoms are really perfect for those working or playing in really cold conditions.
Read review: SmartWool Merino 250 Bottom
Best for Lightweight/Aerobic Activity
Outdoor Research Enigma Bottoms
Looking for your next pair of superhero tights? The Outdoor Research Enigma Bottoms might just help you achieve your extraordinary adventure goals. These ultra-lightweight leggings boast an incredible moisture-wicking capability, earning our Top Pick for anyone who thoroughly enjoys running up mountains, or any other highly aerobic activity in the cold months. Built with a proprietary merino/poly-blend, this base layer has the super ability to wick away sweat as quickly as we produced it. Even with their fast-and-light appeal, these bottoms offer the right amount of warmth to fight off the autumn chill when worn alone on an early morning trail run, and just enough insulation to comfortably sleep through colder alpine nights.
This thin pair of long underwear is certainly not designed for standing around on a snowy belay ledge while your climbing partner struggles up their newest ice-project. But for any activity that is going to work up a sweat, in almost any climate, these exceptionally designed bottoms will keep you dry, comfortable, and on the move.
Read review: Outdoor Research Enigma Bottoms
Why You Should Trust Us
Our expert on cold weather-layering systems is Aaron Rice. With an intention to pursue snowy adventure as a way of life, Aaron works as a full-time ski patroller and part-time snow scientist— ask him about stellar dendrites or 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. Also as a Master Educator for the Leave No Trace Center for Outdoor Ethics, Roland has taught land stewardship and environmental ethics courses.
Finding out what long underwear model is best among a large group of contenders started off with internet searches and hours spent reading reviews. We initially considered over 30 offerings from various manufacturers before finally deciding to purchase and test the 9 discussed here, which we considered most promising. Like many products we test, the protocol involved a combination of field use and lab tests. Aspects like warmth, comfort, and fit were evaluated primarily while wearing the underwear in a variety of outdoor settings, while durability and breathability were best served with lab tests, such as the 8-inch granite abrasion test we devised for testing how well the garments resisted abrasion.
Related: How We Tested Long Underwears
Analysis and Test Results
Long underwear — also commonly referred to as base layer bottoms — plays an important role in both keeping you warm and regulating your body temperature while you're out playing in colder conditions. Bottoms aren't used as frequently as tops, often only coming out when the cold of winter really sets in. But don't be mistaken, these aren't designed just for warmth. Long underwear can actually be quite versatile, coming in just as handy for pajamas on a backpacking trip, wearing them as tights while trail running, or layered under your favorite pair of jeans for a night around a bonfire. Of course, they are a non-negotiable layer for colder-weather activities, such as layered underneath a technical shell while out ice climbing and skiing. These base layers work to keep you dry and comfortable by wicking sweat away from your body, a valuable aspect in nearly any outdoor pursuit.
Related: Buying Advice for Long Underwears
We scored each layer across four metrics, which are designed to encompass the traits we believe make long underwear a valuable addition to your wardrobe. These scores — determined through a variety of tests — are then compiled, and we assign a total score out of 100 for each pair of bottoms. These products are tested side-by-side, so it is important to note that these scores are relative to the other products in the review; a low score does not mean that a product is not worth its weight-in-wool. It simply means that it did not perform as well as other products in this review. We evaluated each pair of bottoms based on: Warmth, Breathability, Comfort and Fit, and Durability.
You can easily spend significant amounts of cash on long underwear bottoms, but before you do, consider if that investment is really necessary. 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 looking for a pair to pull on to shovel the sidewalk, you likely have the ability to save some money, and still get your hands on a quality product. Merino wool models, in general, are going to cost more because it is a relatively expensive material to produce. Synthetic models are almost always less expensive, but often provide qualities — such as quick-drying fabric — that may be more important to you. While synthetics tend to accumulate the stink of sweat more easily, they also tend to be more durable than natural fibers through many wash cycles, so their longevity adds to their value.
Our Best Buy Award winner from REI Co-op is a great option for a synthetic pair of bottoms that are just as valuable at home walking the dog on cold winter days as they are carving up groomers on skis. These lightweight bottoms may not sustain you in terms of warmth for long adventures in snowy terrain, but as a lightweight option, they are versatile enough to carry you through the other three seasons when you need to pack a little extra something to layer with. For those really looking to get after it in the backcountry, the OR Enigma Bottoms may just be the future of fast-and-light technology for base layers. These bottoms are knit with a proprietary blend of recycled polyester and all-natural Merino wool, so it is not only sustainably valuable but also offers an opportunity to hop into a performance-minded pair of long underwear at a price-point that falls well below many of our full merino wool options.
Warmth is one of the most significant factors to take into consideration when thinking about adding long underwear to your kit — after all, if we were able to stay warm all on our own, would we even have invented base layers? Well, that's debatable when considering the other benefits of these garments. But it's certainly a major factor and one that we don't accept at face (fabric) value. While we often find a correlation between warmth and thickness of material, it is a more complex question, also taking into account fabric type and fit. A bottom's ability to keep you warm is maybe most importantly rooted in its ability to wick sweat away from your body, keeping you dry and comfortable while active, rather than having your legs end up a pair of cold, soggy noodles at the end of a day.
Not just a necessary element in the middle of winter, we tested these bottoms through a wide range of temperatures and environments in order to accurately review how these bottoms compared to one another. Working up a sweat skinning steep terrain, walking the dog in freezing temperatures, winter hiking, fall backpacking, and sleeping in the back of the truck or out in a tent through the long, dark, cold nights. Warmth is a dynamic metric because there is a myriad of considerations to keep in mind on a personal basis, such as asking yourself, "how warm do I sleep?" But it is important to be aware that the warmest bottoms aren't always the most practical for your needs. Consider a few factors: what temperature range will you be using them for? What intensity of activity will you be engaging in? Do you want versatility across seasons or just mid-winter warmth? As mentioned above, do you naturally run cold or hot? Finally, are you layering them under a single, technical hardshell pair of climbing pants, or rather under a thick pair of ski pants that already offer a level of warmth and insulation?
If you need bottoms for activities in the bitter cold, we recommend the SmartWool Merino 250, Ortovox Rock'N'Wool, or Arc'teryx Rho LT; in that order based on overall warmth. If you're looking for a great, versatile pair of long underwear, the SmartWool Merino 150, Patagonia Capilene Midweight, Icebreaker Merino 200 Oasis, or the REI Co-op Merino Midweight bottoms are good choices that offer a bit more of a mid-range feel. If warmth isn't as pressing for you, and a lightweight bottom perfect for summer backpacking, cross-country skiing, and winter climbing trips to the desert are more your speed, the REI Co-op Lightweight bottoms may be your ticket. Similarly, if you want a bottom for your SkiMo training, check out the Outdoor Research Enigma bottoms as a great option for those who value moisture-wicking capability slightly more than warmth-by-insulation.
Breathability is a quality that can make or break how effective a base layer when it comes to regulating your body temperature. Regardless of whether you are shedding sweat-pounds breaking trail in waist-deep snow, working hard shoveling the driveway, or running laps around your city in the fall, it is important that you are able to stay dry and comfortable through it all.
A garment's ability to breathe lives in the fibers of the fabric. Breathability is the capacity of the fiber to move heat-induced moisture — i.e., perspiration — from the inside of the garment to the outside, and allowing it to then evaporate from the surface of the layer. This process both keeps you from overheating and allows the bottoms to stay dry when you're working up a sweat. This all adds up to comfort while on the move, and relative warmth throughout a range of body temperatures, increasing versatility for a variety of environments.
Our body temperature doesn't fluctuate as intensely on our bottom half as it does on our top half, but with some of our major working muscles, it 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 you're participating in highly aerobic, start/stop activities, like backcountry skiing. To test breathability, we skinned up windy ridges, ran icy mountain trails, and wore these bottoms in boiling hot huts (a little too much stoke in that wood-burning stove right before bed, buddy…). We wore these layers for months of outdoor activity, only finally convinced to take them off in order to perform a controlled test in the lab, and to shower. Testing these bottoms side-by-side in a temperature-controlled, indoor environment, we worked up a sweat with the same short, rigorous exercise routine — pull-ups, push-ups, mountain climbers, burpees, and jump squats — while wearing each base layer. We noted how well they breathed through bursts of intense activity, and then timed how long it took for our skin to dry after each workout.
Our most breathable layers, not so shockingly, were on the lighter side in terms of fabric weight. The Smartwool Merino 150 and Icebreaker Merino 200 Oasis bottoms are great choices if you are seeking a high level of breathability in a full-merino pair of long underwear. Almost every merino layer we tested offers superior moisture-wicking ability — a natural quality and benefit of merino wool — which promotes the capability for these layers to breathe well while you're on the move. 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 synthetic builds that do a solid job when it comes to moisture wicking, but dry out on the body much faster than all-natural fibers. But the front-runner in our testing was the Outdoor Research Enigma bottom, a hybrid of recycled polyester and merino wool, which combines the best of both fabrics to provide top-notch breathability, and is our Top Pick for high-output activity.
Comfort & Fit
While tops have been given a lot of design attention to promote ease of layering, bottoms are historically notorious for a poor fit. The days of yore offered us no choice but cotton longies that were too baggy in the knees, had an itchy waistband that stretched four sizes by the end of the day, and a crotch that darn-near reached your knees. Well, the wild-west days of long johns are gone! We've entered an era of functional design and technical materials where modern bottoms are comparable to their upper halves, affording options for high performing base layer systems. 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 metric, with ideas about the right kind of fit varying wildly across different body shapes, sizes, lengths, and types. Through analysis of articulation, seam placement, cut, and design features, we do our best to identify any areas of concern that may apply to each and every user, not just the ones that match our own bodies. But with that being said, we always suggest trying things on in-person so that you can decide for yourself if they fit well.
We considered a number of different factors to determine comfort and fit: the feel of the fabric next to skin; how tight or loose they fit in particular zones, such as the knees and cuffs, and how these bottoms fit overall; the stretch and freedom of mobility; the size and comfort of the waistband; the length of the legs, and stretch of the cuffs; the depth of the crotch and any bottom-sag; the type of seam stitch, and the articulation and associated comfort of stitching; and of course, the layering ability of these bottoms. We wore these bottoms for many hours, through many activities — from hanging on the couch reading and sipping coffee, to battling up ice-climbing routes. Armed with a long list of notes and inquiries, we rank each pair to equip you with the best possible knowledge of how these bottoms might fit, to better inform your online purchasing.
We have only tested high-quality products here, so comfort is fairly uniform. These bottoms are all generally soft next-to-skin — particularly any of the 100% merino bottoms, and ones made with recycled polyester — and offer a level of coziness that generally increases with material weight. When it comes to ranking pairs of long underwear side-by-side, it is the fit that sets them apart in this category. If you are looking for that ultra-soft bottom and don't mind a little stretch or sag, the Smartwool Merino 250, Patagonia Capilene Midweight, or REI Merino Midweight bottoms are perfect getting after it, as well as for the down-day hang. The SmartWool Merino 250 blasts the roof off of comfort, with their beloved 250 g/m²-weight cushy Merino wool and super comfy waistband, but has a bit of what we refer to as SCS (Soggy Crotch Syndrome). Pairs that are still going to feel like your favorite pair of sweatpants, but with a little more cut, are the Ortovox Rock'N'Wool or Smartwool 150 bottoms. Our favorites for soft fabrics coupled with second-skin mobility are the Arc'teryx RHO LT and the Outdoor Research Enigma bottoms. Finally, if you're looking to fit in with the yoga or fall-running crowds, the Icebreaker Merino 200 Oasis is a great all-natural option. We also dig the synthetic REI Lightweight Bottoms for shoulder season runs.
Durability has never been a particularly strong suit when it comes to base layers — remember, these bottoms are specifically designed to be worn at the base of your kit. When these layers double as a standalone bottom, such as a pair of running tights, we like to think of it as more of an added bonus. 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. The SmartWool Merino 150, for example, wraps the Merino wool around a nylon core to increase durability. Even some of the pure, 100% Merino options, like the Ortovox Rock'N'Wool bottoms, surprised us with top-notch resistance to abrasion during our aggressive lab testing. Other designers opt to blend polyester fibers with Merino wool to increase product-life, like the Outdoor Research Enigma bottoms. While synthetic fibers are traditionally more durable, we found in our testing that the thinner, lightweight bottoms, regardless of material build, are the most susceptible to damage. Both the Smartwool 150 (mostly merino wool) and the REI Lightweight bottoms (fully synthetic) were two of only three layers to sport holes after our abrasion test. While this may be an obvious finding to many of you out there, it is worth noting that none of the heavier-weight options — with the exception of the REI Merino Midweight — produced holes after the same testing process. What we're getting at is that material type, while still a factor, is beginning to take a backseat to fabric weight when it comes to durability.
Not able to break that material stereotype just yet, the most durable pair of long underwear we tested are a pair of synthetic bottoms. The Arc'teryx RHO LT is by far the most durable of all the layers we tested, with a brushed-nylon face fabric that showed very little wear after both laboratory and extensive field testing. Of the merino layers, the thick fabric of the SmartWool Merino 250 is the most durable, and the slightly thinner Ortovox Rock'N'Wool pants produced similar durability results.
Long underwear bottoms are not an article of clothing that you tend to buy on a seasonal basis, or often own multiple pairs of for that matter. We agree that it is worth doing some research, armed with the knowledge of how you intend on using this particular piece of gear, to land a pair that is perfect for your work and play, and will hold value through years of use. Remember, it is important to consider factors like your personal temperature-disposition and the range of temperatures you plan on wearing them in, and the types of activities you are purchasing these bottoms for. Your personal considerations, combined with our meticulous obsession for gear, will hopefully pair you with a new set of bottoms that will keep your buns toasty and the stoke high for years to come!
— Roland Mott and Aaron Rice