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Our backcountry clothing experts have tested 34 pairs of the best long underwear for women over the last 7 years, with the top 13 of the market's most promising in this review. Each next-to-skin layer has seen bucket loads of sweaty missions from backcountry splitboarding to multi-pitch rock climbs to ultra trail runs over snowy trails — all in pursuit of finding the warmest, most breathable, and most comfortable pair. We test across North America, from the sandstone desert of Utah to the high mountain ranges of Alaska and California, throughout the colder half of the year. After meticulously comparing each product, we provide you with our insights to offer honest recommendations that will satiate your thirst for outdoor winter adventures.
Editor's Note: We updated this review on November 22, 2022, to include more information on our testing and scoring methods, new offerings from Ortovox, Ridge Merino, Kari Traa, and REI Co-op, as well as the latest iterations of some old favorites from Icebreaker and REI.
The Icebreaker BodyfitZone Merino 260 Zone Thermal Leggings are the top performer for individuals who like to remain active in the colder half of the year. The naturally-odor-resistant merino wool fibers create a comfortable next-to-skin feel, and a brushed elastic waistband keeps these leggings in place during cold-weather activity. We also love that Icebreaker added a touch of elastane to this legging, so they move with you throughout the day, whether you are out for a backcountry ski mission or hanging around the cabin and stoking the fire. We are super impressed by the ventilation panels, based on Icebreaker's new BodyFitZone technology, that are strategically placed behind the knees and at the lower back to allow for superior breathability and thermoregulation. These leggings are technical yet remain extremely comfortable.
The high price is the biggest hindrance here. Although they are one of the most expensive pairs of long underwear that we tested, we truly believe you get what you pay for. In this case, a long underwear bottom of exceptional quality, fit, and the ability to keep you warm and dry during cold weather sending.
Our testers were psyched to include the Ridge Merino Inversion Heavyweight Merino Leggings as part of our fall update. If you've wanted a Merino base layer but the price makes you cringe, these leggings have super soft 100% Merino wool fabric and a heavyweight design at an extremely competitive price. The ultra-fine 18.5 gauge Merino wool feels noticeably soft next to the skin, while the high elastic waistband provides more coverage and structure to the wool design. Our testers deem the fit true to size, the fabric naturally odor-free (even after several uses between washings), and we experienced no durability issues during our extensive testing period.
While these long johns perform super well in the cold conditions for which they were created, we noticed limited breathability during the warmer months of the year. Although perfect for those colder nights in the fall and certainly excellent for the depths of winter, we don't recommend these leggings for year-round use due to their thickness. Perhaps the only other complaint would be that the light color we tested can pick up the color of other darker fabrics that are layered over the top. Overall, these heavyweight leggings impressed our testers with their excellent comfort and remarkable warmth, whether chilling at camp during the fall or getting after it during the winter.
Less comfortable compared to natural Merino fabrics
Polyester fabric retains odor immediately
The REI Co-op Midweight Tights offer great synthetic performance at an affordable price. The blended polyester and spandex fabric feels incredibly soft against the skin and features a four-way stretch that allows for full range of motion. While more of a lightweight fabric, these tights offer ample warmth for the shoulder seasons and when paired with thicker insulation for the colder months of the year. Featuring a fit that's true to size as well as durable flatlock seams, these tights are a great choice for a variety of cold weather activities.
Unfortunately, we were not impressed by the garment's ability to release moisture from the fabric after some high-intensity activities. While these tights were able to wick sweat away from our skin, we noticed that it pooled near the waistband and took a longer amount of time to dry. We also noticed that the fabric retained odor almost immediately after our testing period started. These things aside, these synthetic tights impressed our testers with a competitive performance, especially considering the modest price tag.
The Ortovox 185 Rock'N'Wool Short Pants are the perfect pair of long underwear for those looking to reduce the bulk inside of their ski boots. The 100% Tasmanian wool feels super soft against the skin and provides ample thermoregulation. The European-inspired design features a bright, thick, and functional waistband and multi-colored yarn to up the style points. Our testers love this layer for how well it breathes yet retains warmth during higher-intensity missions.
The only caveat to these short pants could be their overall durability. While we did not experience anything beyond minor piling in high-traffic areas and the fabric stretching when worn multiple times between washes, we speculate that the trade-off for this ultra-fine Merino is that it won't last as long as its synthetic competitors. Overall, our testers consider these short pants to offer high performance in a lightweight Merino wool package.
Known for its durable design, the Patagonia Capilene Midweight Bottom once again rises to the top for synthetic performance. Constructed of 100% recycled polyester, this pant has a midweight construction and is versatile enough to wear during all four seasons. The smooth-face fabric retains its shape while providing efficient thermoregulation, and the material is thin, easy to layer, and boasts all-day comfort. The synthetic fabric also offers superior durability with wicking power that's hard to compare.
Unfortunately, synthetic materials simply aren't as cozy as Merino wool. The fabric (despite its treatment) also gets smelly after a few days of use, so it's not our top choice for multi-day missions. However, if you are seeking a highly durable synthetic pair of long underwear at a great price, the these will not disappoint.
Lightweight material can tear if you're not careful
At 3.1 ounces, the Odlo Performance Light Bottoms are the lightest pair of long underwear bottoms we tested. This pant is built for picking up the pace in cool to cold weather, featuring synthetic materials with ventilation panels throughout the length of the legging to offer superior wicking ability and thermoregulation. Because the material is so lightweight, we recommend this layer to provide extra warmth during trail runs at the change of season or nordic skis during the winter months.
We experienced no durability issues with these bottoms during our testing period. However, the material is so lightweight that we can imagine they could snag if not properly cared for. We also do not recommend sizing up, as the snug fit is meant to hug your curves and allow for easy layering. The Performance Light Bottoms are a solid option for the athlete looking to maximize performance year-round, available at a reasonable price, too.
When testing women's long underwear, we consider the different ways each bottom can be useful. We take stock of what's on the market, selecting the highest-rated products with the best reputation. Then, we buy each layer at retail price and test them side-by-side for months at a time. We've spent the last four years searching for the best pair of long underwear bottoms, which allowed us to record our experiences throughout all the possible cold weather conditions. We've taken each model on international trips and used each locally while climbing, biking, and exploring Colorado's San Juan Mountains and California's Sierras. After our field tests, we evaluate each product, score it, and share our findings and thoughts.
Our testing is divided across four key metrics:
Warmth (30% of total score weighting)
Breathability (30% weighting)
Comfort and Fit (30% weighting)
Durability (10% weighting)
This review was spearheaded by Amber King, an outdoor educator and adventurer. When climbing, snowboarding, hiking, sailing, and trail running, she's commonly wearing a great pair of base layer bottoms to keep her warm and comfortable, from the Faroe Islands to the Cordillera Huayhuash of Peru. After spending a very cold decade in the Tetons and recently migrating to the Eastern Sierra, Trish Matheny knows what she's looking for in long underwear performance and rounds out our testing team. An avid rock climber, trail runner, and born-again splitboarder, Trish wears base layers almost daily when pursuing her passions amongst the elements. She hopes that by sharing her experiences, she can offer thoughtful recommendations to help you select the best layer for your backcountry adventures.
Analysis and Test Results
A solid long underwear bottom is a key part of any outdoor wardrobe. Designed to sit next to the skin, it should wick away moisture to keep your skin warm and dry. While each bottom can be used on its own in warm weather, it is typically used in a layered system during the colder months of the year. To find the best pair for different activities, we look at a range of base layer bottoms in a variety of weights, from light to heavyweight.
There are many great options out there that won't cost you an arm and a leg. When considering value, it's important to consider both performance and durability. The Ridge Inversion is constructed from 100% Merino wool and boasts one of the lower price tags of its competitors. Our testers were impressed by the incredible comfort, warmth, and durability offered by these affordable and simple leggings.
The Patagonia Capilene Midweight is our top choice for an overall excellent synthetic workhorse, followed closely by Odlo Performance Light Bottoms — and both come in at a reasonable price. We were also impressed by the performance of the REI Co-op Midweight, especially considering it has one of the lowest price tags in this entire review. However, all three are constructed out of synthetic materials, which are typically not as warm as Merino wool.
The Icebreaker 260 Zone Legging and the 185 Rock'N'Wool Short Pants are fantastic choices for those seeking 100% Merino — if you can afford to cough up the not-insignificant extra cash. While the Icebreaker Legging is the most expensive design in this review, we feel these leggings are worthy of the investment.
Look for last year's colors on your favorite and more expensive long underwear bottoms. You can typically find them at a discount with the same great performance.
The insulative warmth of a base layer bottom balances with breathability to provide great thermoregulation. When looking at warmth, you should know that most models are available in different fabric weights. The higher the fabric weight, the warmer it is supposed to be. However, we've come across plenty of layers that claim to be heavyweight but perform closer to a midweight construction or midweight layers that perform as you'd expect from a lightweight design. More likely, you'll see a fabric advertised as "lightweight" that is actually fairly thick and performs at a midweight level. To help you navigate marketing claims, we provide side-by-side comparisons and let you know our opinion of the effective fabric weight offered by each pair of long underwear.
When it comes to warmth, there are two different schools of thought. The first is that a warmer base layer will lead to greater warmth overall. The second is that a base layer bottom should be as thin as possible, utilized just to wick away moisture, while a fleece or other layer will provide the additional warmth needed to withstand the elements. While neither is right or wrong, what you buy is based on your personal needs and preferences, so be sure to decide what you prefer before making your final decision.
During our testing period, we perform a few different tests. First, we observe the fabrics and construction of each product, assessing the tightness and relative thickness of the fabric weave. Then, we test warmth by playing and working in cold and windy weather before sleeping in each pair under the stars on frosty nights. We carry our base layers with us, cycling them out to see which offers the best insulation and warmth as a stand-alone piece or underneath a pair of pants. We record our experiences, compare notes, and report back to you.
Through extensive testing, we learned that the natural organic fibers of Merino wool feel amazing against the skin and also offer the best range of thermoregulation and warmth for the coldest days of the year. Merino wool base layer bottoms, like the Ridge Inversion, the Meriwool Merino 250 Bottom, and the Smartwool Classic Thermal Merino offer the most warmth with thicker fabrics that wick moisture and insulate very well on cold days.
The 260 Zone Leggings are the perfect marriage of warmth and breathability. The 260 g/m² fabric keeps you warm, while the strategically placed ventilation panels allow for maximum breathability, so you don't overheat or get too sweaty during activity. While the Icebreaker 200 Oasis Leggings have 200 g/m² of Merino wool, they actually feel pretty light when wearing them, perhaps due to the airflow through the ventilation. The Oasis is still very warm and insulates well in colder weather, but if you're seeking the warmest model, go for the Ridge Inversion.
While synthetic long underwear bottoms typically do a great job of drying quickly and staying cool, they usually aren't as warm as Merino wool. Some new synthetic bottoms are getting close, though. The Patagonia Capilene Thermal Weight Bottoms is a pretty warm option loaded with a polyester-spandex construction. They are warmer than the Patagonia Capilene Midweight, given their thicker fabric and a higher level of insulation. This bottom generates more warmth with wear, but it feels a little chilly at first, especially on those cold and dark winter mornings.
The synthetic Odlo Performance Light Bottoms are great for maintaining the heat generated during workouts and outdoor activities. However, they would not be a good choice for sedentary pursuits like hanging around a winter base camp or riding the chairlift. These bottoms perform best during more intense activities such as Nordic skiing or winter training runs.
Breathability and wicking capabilities work together to ensure your skin stays dry, whether you're pushing the aerobic threshold or merely hanging out by the fire. To test breathability, we look at fabric thickness and type. We take each option running, hiking, climbing, and biking in both warm and cold weather. We then look at the fabric to see if any moisture is retained in the fibers or if it's able to stay dry.
It's not surprising that the fastest base layer bottoms to dry are the thinnest. Thinner materials allow air to pass through more readily, thus facilitating evaporation. The best breathers of the group are the Icebreaker 260 Zone Leggings, Odlo Performance Light, and the 185 Rock'N'Wool Short Pants. These are all good choices for trail running, rock climbing, or backcountry ski missions. We prefer the 260 Zone Leggings when the temperature is decidedly cold (near to below freezing) and the Odlo Performance Light for cool to cold weather (40 to 60 degrees Fahrenheit). The Icebreaker and Odlo score a bit higher than the Ortovox 185 because they have special ventilation zones that target specific areas of the lower body that tend to store heat and sweat (lower back and behind the knees). These body-mapped ventilation panels work well to promote airflow in these areas, removing moisture and keeping them a little cooler than the rest of the legs.
Following in breathability are the synthetic competitors. Synthetic fabrics are known for their rigid structure that typically wicks well and dries quickly. An exception to this rule is the REI Co-op Midweight which didn't breathe as well as we would have liked, often retaining sweat in the waistband and requiring more time to dry fully. Synthetic fabrics are typically more porous, too, except the REI Co-op Midweight features a tightly woven and slim-fitting polyester fabric. On the trail, we prefer synthetics such as the Patagonia Capilene Midweight and the REI Lightweight Base Layer Tights, which offer a mostly porous and thinner lightweight construction which will dry faster on the trail or ski tour.
Both Patagonia Capilene models actually have a similar drying speed. Even though the Patagonia Capilene Thermal Weight has more material and absorbs more water, it can transfer moisture just as well as its thinner sister. If we had to choose one for running or super aerobic activity, we'd opt for the Capilene Midweight as it doesn't hold any moisture in the fabrics and is a much thinner construction.
Thicker base layers like the Smartwool Classic Thermal and Meriwool Merino 250 offer strong breathability but are not as quick to dry. While they are thicker in construction, if worn with a pair of pants that lack ventilation so moisture can accumulate inside of the fabrics, and that build-up can lead to a much colder experience. When this moisture buildup occurs, the wool contenders typically perform best because wool can retain heat, even when wet, much better than thicker synthetic fabrics. That said, with adequate ventilation, both are built to breathe well. Consider these thicker weights for activities such as nightly winter dog walks, hanging out in the yurt next to the fire after a day of backcountry skiing, or keeping you warm on the chairlift on the coldest days of the winter.
Comfort and Fit
A long underwear bottom that'll feel cozy from the ski hill to your bed is the best you can ask for. One that fits correctly will also offer the highest level of comfort throughout the entire day of adventure. So, we take the time to evaluate comfort and fit. To test, we put each bottom on, wear it all day, and record our experience with each base layer. We chill out by the fire, we sweat, we drink coffee, and we do yoga in the sunshine. We determine which feels great against the skin, which begins to lose its shape, and which we would recommend to size up or down.
Our go-to layer for comfort and fit, no matter what activity we had planned for the day, is the 260 Zone Legging. This layer fits our bodies true to size, with a brushed elastic waistband that doesn't inhibit comfort or range of motion during activity or while sleeping. We love that the designers at Icebreaker gave these leggings a little bit of elastane that allows them to maintain their shape and move with us during our winter training or while catching up on sleep during those long winter nights.
The Smartwool Classic Thermal bottoms are also quite comfortable. These bottoms are thick enough to keep you warm and provide enough coverage to be worn on their own; however, the fabric eventually sags throughout the day and doesn't have enough shape to hug your curves. Like many other Merino wool contenders, it's best worn underneath another layer or as loungewear around the house. Our testers love the Ridge Inversion, which features a high-waisted design for added coverage and a functional yet comfortable thick elastic waistband. Other lighter Merino wool bottoms like the Icebreaker 200 Oasis and the Ortovox Rock'N'Wool are also super comfortable and have a softer feel next to the skin, thanks to their 100% Merino wool fabric.
Since the fibers utilized in synthetic material are often hollow, they get colder quickly, which means the materials feel colder when putting them on in the morning. Of synthetic competitors, we like the Patagonia Capilene Midweight and the Odlo Performance Light Bottoms the most. The thinner fabrics, like the Odlo, are still soft against the skin but should be worn during activities that generate a lot of heat.
We understand that durability is key when purchasing a product that is essential for your winter kit. You don't want to invest in a pair of bottoms only to find out that they fray and wear out after only a few uses. To test for durability, we observe wear and tear throughout our testing period and continue to test until a new iteration of the product is developed. We bike, ski, climb and run with each pair of long underwear and record our experiences while layered under thicker fabrics or simply worn on their own. We evaluate the quality and craftsmanship of every product by looking at its seams and stitching. After walking through brambles, sliding through canyons, and hiking with snow pants, we get a good idea of durability from each product. We continue to update this section throughout the year as we gather more information.
If the most durable bottom out there is what you want, look for thick fabrics made from synthetic materials. These strong fibers are stiffer, providing better resistance to abrasion and stretch than Merino wool. The most durable pieces we've tested so far are the Patagonia Capilene options. We tested these bottoms for several years and are happy to report they are still looking great after hundreds of miles and intense use on the trails.
While the Capilene layers are great options for performance and durability, we noticed that the Midweight does not perform quite as well as the Thermal Weight. This isn't surprising because the Thermal Weight is constructed from a much thicker fabric weight. The REI Co-op Midweight Tights feature durable polyester and flatlock seams which inspire confidence in their construction, if only they didn't smell after minimal use.
We were perhaps the most curious as to how the Odlo Performance Light Bottoms would hold up during intense activity in the elements and are pleased to report that we experienced no durability issues during our testing period. At only 3.1 ounces, they are the lightest material that we tested, and after several trail runs through sage and rabbitbrush, we observed no snags or tears in the extremely thin and breathable material. Still, we are hesitant to call this pair "robust" and continue to take extra care of these bottoms.
While Merino wool isn't as durable as some synthetic fibers, it's not like it will fall apart easily. Bottoms that integrate both Merino wool and synthetic fibers into their construction, such as the 260 Zone Leggings, tend to hold up to wear and tear much better than their 100% Merino wool competitors.
A thicker construction is seemingly more durable than a thin one. However, these thicker contenders actually tend to snag more easily and pill faster than thinner options. Of the Merino wool bottoms made only with this fabric, the Icebreaker 200 Oasis proves to be the best. The material is tightly knit, and even for its thinner construction, it seems super burly. Close behind is the Kari Traa Rose High Waist Pant featuring a durable, thick, and well-made design reinforced with flatlock seams. Another impressive 100% Merino wool design is the Ridge Inversion which held up to rigorous use rather well.
Our testers were disappointed in the Smartwool Classic Thermal that started to show signs of wear after very minimal use. This former high-scoring pair began to unravel after only a few nights of sleeping and one trail run during testing. Most other Merino designs in this review showed no major signs of wear; however, this is a good example of Merino wool being more susceptible to failure versus a more durable synthetic failure that may hold up a little longer.
We've come a long way since long underwear was made from super thick, itchy wool or a cotton dimpled suit. With so many options to choose from, it's important that you take the time to select the piece that'll not only offer a high level of comfort but also meet your performance needs. We hope our in-depth research has assisted you in your quest for the perfect base layer and that you stay warm and dry throughout the colder months of the year.
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