We combed through 30+ of the best long underwear bottoms and chose the 6 most intriguing men's models of 2019 to test head to head. Our experts tested these bottoms on a wide array of adventures and across a spectrum of environments and temperature ranges, from fall river trips in Utah to winter trail runs, hikes, and climbs in the Rockies to wind-blown ridgelines in the Cascades. Our legs have become well acquainted with these pups and their ability to keep us warm, breathe, and take a beating, and we did it all to provide the in-depth info you need to help you choose the best pair of bottoms for your outdoor ventures.
The Best Long Underwear Bottoms of 2019
|Price||$89.00 at Amazon||$74.99 at Backcountry|
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|$89.00 at Backcountry|
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|$56.99 at Backcountry|
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|$79.50 at REI|
|Pros||Warm, lightweight, great breathability, versatile, quick to dry, anti-odor, great fit||Extremely warm, super cozy, terrific temp regulation, breathable||Warm, super comfy, durable, great fit, versatile, don’t stretch out||Warm, lightweight, breathable, versatile, comfortable, great thermoregulation||Comfy, warm, simple, breathable|
|Cons||Not super durable, not for super cold||Stretches out, soggy crotch, slow to dry, expensive||Pricey||Not very durable||Not very durable, tend to stretch|
|Bottom Line||A go-to, do-it-all merino base layer that provides superb insulation, incredible breathability, and a dialed-in fit for high performance in any situation you can dream up.||An extremely warm and breathable pair of bottoms built to keep you warm in the coldest conditions but versatile enough to carry into seasons outside of winter.||An outstanding synthetic bottom that offers great warmth, extreme comfort, a stellar fit, and durability to last; built for cold conditions these cozy bottoms are perfect for everything from winter trail running to cold resort skiing.||A fantastic pair of lightweight merino bottoms that provide impressive warmth without being too hot, breathe extremely well and are very comfortable.||A simple and comfortable merino option|
|Rating Categories||Alpine Onset Bottoms||SmartWool Merino 250 Bottoms||Arc'teryx Rho LT Bottoms||SmartWool Merino 150 Bottoms||Merino Midweight Bottoms|
|Comfort And Fit (30%)|
|Specs||Alpine Onset Bottoms||SmartWool Merino...||Arc'teryx Rho LT...||SmartWool Merino...||Merino Midweight...|
|Material||83% merino wool, 12% nylon, 5% spandex||100% merino||Torrent (84% polyester, 16% elastane)||87% Merino Wool, 13% Nylon Core||Ultra-fine 200g merino wool|
|Weight (size S)||4.80 oz||7.55 oz||5.57 oz||4.94 oz||5.93 oz|
|Fabric Weight||Not listed||250g||Not listed||150g||200g|
|Fabric weights and other versions available||Lightweight||Lightweight, midweight||Boot-cut||150, 250||Midweight|
Best Overall Long Underwear
Outdoor Research Alpine Onset Bottoms
Striking an impressive balance between warmth and breathability, the Outdoor Research Alpine Onset Bottoms have taken hold of our hearts this snow season. The light-ish weight merino wool reinforced with nylon and spandex for durability and stretch offers an extremely versatile bottom that excels in a myriad of situations. Breathing like a champion, wicking away sweat like a boss, and staying dry when the interior furnace is running at max heat but also keeping us warm when we tucked and hucked downhill in dumping snow, this bottom proves itself to earn our Editors' Choice Award. It seals the deal with a thoughtful and minimalistic design and a terrific fit.
As with all merino wool layers, durability is a crutch. The nylon reinforcement of the merino fibers does help a bit with durability but not enough to make us run around the streets joyously professing that all is right in the world. The waistband is comfortable and does a great job of not rolling on itself but it's not the coziest on the market. Again, as with all merino, the fabric tends to stretch. This wasn't a major concern with these bottoms but we noticed that the waist and thighs held true through use but the bottoms stretched out if they were worn over thick socks or pulled up onto your calves. Overall these long underwear bottoms perform beautifully in high-intensity activities in the cold as well as mellow evenings at the cabin. We recommend them for anyone that needs a versatile do-it-all pair of bottoms that will excel in everything from backcountry skiing to summer alpine backpacking.
Read review: Outdoor Research Alpine Onset Bottoms
Best Bang for the Buck
REI Co-op Lightweight Bottoms
If you're looking for a pair of longies to assist you in your pursuit to crush but you don't want to empty your pocket to do it, look no further than the REI Co-op Lightweight Bottoms. For about a week's worth of Pumpkin Spice Lattes, you can own a comfortable and quality pair of bottoms. The smooth and lightweight synthetic material is comfortable, durable, and boasts a really terrific fit. The lightweight polyester dries quickly and is ideal for three season use or four seasons if you run on the warm side. An honest work ethic and versatile application from summer camping trips to high output activities in cooler weather make these bottoms hard to beat for the price point.
Synthetic fabrics are notorious for being smelly. REI incorporates a Mineral-based LAVA XL™ finish that helps keep these bottoms from acquiring stink so quick. Even with the finish, these are going to be more susceptible to funk than a merino layer but we applaud and appreciate the effort. The polyester fabric dries extremely fast but doesn't quite breathe as well as merino layers. Being such a lightweight fabric these are not made for deep winter ventures but are perfect if you need a versatile and comfortable pair of longies to accompany you on outings in every situation but deep cold. Overall we are extremely impressed with the quality, comfort, fit, and unbeatable price of these bottoms!
Read review: REI Co-op Lightweight Bottoms
Top Pick for Warmth
SmartWool Merino 250 Bottoms
If you read the review for the SmartWool Merino 250 top you know how we feel about this fabric! The warmth and comfort of the thick and cush 250 gram, 100% merino wool are unparalleled. These bottoms balance extreme warmth and breathability with grace and comfort that is worthy of praise. Built for the coldest conditions but wicking away sweat and breathing so well that they perform just as beautifully when the temps warm up a bit. Flatlock seams and a wide merino covered waistband offers all-day comfort. With a bonus of merino's natural anti-odor abilities, 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 the most durable merino layer but it's still not bulletproof and requires a level of care that is beyond most pieces of gear. These bottoms tend to stretch out after use which we don't love. The fabric will recover from its stretch after a wash but washing them less means they will last longer. 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. For there not to be an extra pocket of fabric below your crotch, the impressively comfortable waistband must be worn above the belly button. These bottoms are perfect for those working or playing in extreme cold conditions and anyone that needs a versatile layer that can not only perform in warm and cool weather but also proves itself in bitter temps.
Read review: SmartWool Merino 250 Bottom
Why You Should Trust Us
Outdoor Educator and guide Roland Mott authors 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. He currently co-directs wilderness courses for a Colorado-based experiential education program.
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 6 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, or base layer, bottoms play an important role in keeping you warm out in the cold and regulating your body temperature while you're crushing in colder conditions. Bottoms aren't used as frequently as tops but when you need them, they're a lifesaver and quite versatile too. Wearing them as tights while trail running, layered under your favorite pair of jeans for a night out, or underneath a technical shell ice climbing and skiing, they are a non-negotiable layer for colder activities.
Related: Buying Advice for Long Underwears
We tested bottoms across a range of activities, temperatures, and environments to understand how they stacked up to one another across four metrics. Testing each bottom's capacity for warmth, breathability/drying speed, comfort and fit, and durability, we put these bottoms through the wringer so you can choose the best pair for your needs.
You can easily spend up to $100 or more on long underwear bottoms, but before you do, consider if you really need to. 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 level is easier to justify. However, if you're looking for a pair to slap on under your ski pants for something cozy next-to-skin for some resort laps, you can keep the price range lower. Just don't drive your price line so low that you reach for cotton bottoms — we don't recommend those. Merino wool models are going to cost $70 and up, in general, because it's a relatively expensive material. Synthetic models are almost always less expensive. On top of that, they tend to be more durable than natural fibers, so their longevity adds to their value. Our Best Buy Award winner from REI Co-op is a totally fine pair of bottoms that are at home walking the dog on cold winter days and carving up groomers on skis, and the price is very reasonable. We don't recommend buying this type of product used to save a few bucks, but hey, you do you.
Warmth is one of the most significant factors to take into consideration when thinking about base layer bottoms. At OutdoorGearLab, we don't accept warmth at face (fabric) value; it's more complex than just the thickness of the material. A bottom's ability to keep you warm stems from a few factors: the thickness of the fabric, yes, but also its ability to breathe and wick sweat away from your body keeping you dry and comfortable across a diverse range of activities and temps.
To provide you with an accurate review of how warm these bottoms are compared with one another we made sure to test them in a wide range of situations. Working up a sweat skinning steep terrain, walking the dog in freezing temps, winter hiking and backpacking, and sleeping 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, but the warmest bottoms aren't always the most practical. Things to think about are: what temperature range will you be using them for, what intensity of activity will you be engaging in, do you want versatility across seasons, do you naturally run cold or hot, or are you wearing them under a technical hard shell layer, like ski pants, that traps heat well and isn't super breathable?
If you need bottoms for static activities in the bitter cold, we recommend the SmartWool Merino 250 or Arc'teryx Rho LT. If you're looking for a great all-around versatile bottom, the Outdoor Research Alpine Onset, SmartWool Merino 150, or REI Co-op Merino Midweight bottoms are a good choice. 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.
Breathability is a quality that can make or break how effective a base layer is at regulating your body temperature, keeping you warm in the cold, cool when your busting chops, and 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 or perspiration from the inside of the garment, transferring it to the outside, and then allowing it to evaporate. This process keeps you from overheating and allows the bottoms to stay dry when you're working up a sweat which all adds up to comfort while moving and relative warmth throughout a range of body and outside temps.
Our temperature doesn't fluctuate as intensely on our bottom half as it does on our top half, but it is an area that is good at producing consistent heat. So having long underwear that will dump heat and stay dry is important when you're participating in high aerobic, start/stop activities like backcountry skiing. To test breathability we skinned up windy ridges, ran icy mountain trails, and wore bottoms in boiling hot huts (a little too much stoke in that wood burning stove right before bed, buddy). In addition to never taking them off for months except to occasionally shower, we also performed a controlled test in the lab. One at a time and in a temperature-controlled, indoor environment, we work up a sweat with the same short but rigorous exercise routine, consisting of pull-ups, push-ups, mountain climbers, burpees, and jump squats while wearing each base layer. We then time how long it takes for our skin to dry after stopping.
Our most breathable layers, shockingly, were on the lighter side of fabric weight. The merino Outdoor Research Alpine Onset and SmartWool Merino 150 bottoms are great choices if breathability is a top factor for you. All the merino layers we tested are great at breathing, a natural quality and benefit of merino, but the two mentioned stood out above the others with their ability to breathe, wick away sweat, and dry quickly next to your skin.
Comfort & Fit
Long underwear bottoms are historically notorious for a poor fit. The days of yore gave us no choice but cotton longies that were baggy had a 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 and we've entered an era of functional design and technical materials. Comfort is a metric that is reasonably uniform across different users but fit is very objectively based and differs wildly between varying body shapes, sizes, lengths, and types. We try to give you an idea of how a garment generally fits so as to not have a bias to any one body type, but with that being said, we always suggest trying things on in-person to see if they fit you well.
Considerations we took into account for comfort and fit were: the feel of the fabric next to skin, how tight or loose it fit throughout, the stretch and mobility, comfort of the waistband, itchy tags, length of the legs, the infamous crotch sag, type of seams as well as design, efficiency, and comfort of stitching, its layering ability, and the general fit. Armed with a long list of skeptical inquiries, we broke down the comfort and fit of each to equip you with the best knowledge of how comfortable and well fitting these bottoms are. We'll let you know if they fit too baggy like your JNCO pants in middle school or too snug like that one time, also in middle school, you tried on your sister's pleather tights while she wasn't home (you didn't think we knew about that, did ya?).
Comfort is pretty uniform across the bottoms, they are all soft and cozy next to skin but the fit is what sets them apart in this category. Our favorites for fit are the Arc'teryx RHO LT and the Outdoor Research Alpine Onset bottoms. Both with a simplistic design, great mobility, super comfortable fabrics, and a thoughtful fit these bottoms wear like a second layer of skin. The SmartWool Merino 250 blasts the roof off of comfort with their beloved 250 weight soft cush merino wool and super comfy waistband but has a bit of what we refer to as SCS (Soggy Crotch Syndrome).
Durability has never been a strong suit when it comes to base layers. The inherent benefits of merino wool are so significant when it comes to performing well in any and every condition that you throw at them but they are just simply not champions of durability. Brands are making strides to enhance the durability of merino wool like the SmartWool Merino 150, for example, wraps the merino around a nylon core to increase durability while others blend nylon and spandex into the merino wool to increase potential longevity like the Outdoor Research Alpine Onset bottoms. These are steps in the right direction and are helpful but the truth is long underwear simply isn't your toughest piece of gear. Synthetic fabrics are generally more durable but don't usually breathe and regulate body temperature as well as merino and are notorious for being stinky.
Not surprisingly, the most durable base layers we tested are the synthetic bottoms. The Arc'teryx RHO LT is by far the most durable of all the layers we tested showing very little wear after the abrasion test. Coming in right behind are the REI Co-op Lightweight bottoms. Of the merino layers, the thick fabric of the SmartWool Merino 250 is the most durable and the least durable which are now not-so-proud owners of holes in their fabrics are the thinner SmartWool Merino 150 and REI Co-op Merino Midweight.
Long underwear bottoms are not something you buy often or own multiple pairs of, so we agree with you that it's worth getting the pair that is just right for you and how you like to play outside. We've compiled an in-depth review to help you do just that. Remember to consider your personal internal temperature disposition as well as what temperature ranges and activities you'll be using them for. Your personal considerations combined with our meticulous obsession with reviewing are great partners in getting you into a pair of bottoms that will keep the buns toasty and the stoke high for years to come!
— Roland Mott