Our Editors independently research, test, and rate the best products. We only make money if you purchase a product through our links, and we never accept free products from manufacturers. Learn more
Our backcountry clothing experts have tested dozens of the best long underwear for women over the last 4 years, with the top 10 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 ultra trail runs over snowy trails, all in pursuit of the warmest, most breathable, and most comfortable base layer leggings. We test across North America, visiting the high mountain ranges from Alaska to Colorado throughout the colder half of the year. After meticulously comparing each product, we provide you with our insights to offer honest recommendations to satiate your thirst for adventure.
The Icebreaker Merino 260 Zone 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 lycra 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.
The Kari Traa Rulle High-Waist is heralded as a value pick by our testing team. Made for women by women, this layer has similar thermoregulation typically offered by more expensive options but at an affordable price. We love how this modern fit hugs our curves thanks to the body-mapping technology utilized for the design. These bottoms are super cozy and comfortable next to the skin, more so than other synthetic options that we tested. The Kari Traa Rulle is a great full coverage option for style and insulation, from the yoga studio to the chairlift.
Unfortunately, you have to sacrifice a bit of breathability and warmth for this lower price tag. We do not recommend this pant for high-intensity adventures nor to be worn during the depths of winter. The Kari Traa does not compare to the Icebreaker 260 Zone Leggings when it comes to performance and maximum breathability. However, the Kari Traa Rulle gets the job done while also standing out for its modern style, cozy next to skin feel, and sufficient breathability, all at an affordable price.
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 provides 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 Patagonia Capilene Midweight 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 Odlo Performance Light Bottoms are a solid option for the athlete looking to maximize performance year-round, available at a reasonable price, too.
Amber King is an outdoor educator, adventurer, and gear tester. 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. 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.
When testing long underwear bottoms, 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.
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. We look at a range of base layer bottoms in a variety of weights, from light to heavyweight. Testing each side-by-side, we evaluate each product using four key metrics: warmth, breathability, comfort, and durability.
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. While the Meriwool Merino Thermal Pants boasts one of the lowest price tags, this Merino base layer bottom can't hold a candle to the durability of other Merino options featured in this review.
The Patagonia Capilene Midweight is our top choice for an overall excellent synthetic workhorse, followed closely by Odlo Performance Light Bottoms. However, both are constructed out of synthetic materials, which are typically not as warm as Merino wool. The Smartwool Merino 250 Bottoms and Icebreaker models are fantastic if you want 100% Merino and can cough up a little extra cash, but our favorite high-value hybrid is the Kari Traa Rulle High-Waist. Comfortable with just the right blend of synthetic and Merino, this pant also comes at a more-than-fair price.
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. That said, we've come across plenty of layers that claim to be heavyweight but perform closer to a midweight construction. 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 and sleeping under the stars on frosty nights. We carry our base layers with us, cycling them out to see which offers the best insulative 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 Meriwool Merino Thermal Pants and the Smartwool 250 Bottoms, offer the most warmth with thicker fabrics that wick moisture and insulate very well on cold days.
The Icebreaker 260 Zone Leggings are a perfect marriage of warmth and breathability. Although a heavier weight than the Smartwool Merino 250, the 260 g/m² fabric keeps you warm, while the strategically placed ventilation panels allow for more breathability, so you don't overheat or get too sweaty during activity. And 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 Smartwool Merino 250.
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 are 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. While this bottom generates more warmth with wear, at first, it feels a little chilly, especially on those cold and dark winter mornings.
Made out of 69% polyester, 27% polyamide, and 4% elastane, the Odlo Performance Light Bottoms are great for maintaining the heat generated during activity. However, they would not be a good choice for sedentary activities 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. If you're looking for a thicker synthetic option that offers enough warmth to be worn without the insulation of a midweight layer, consider the Patagonia Thermal Weight, which has a thicker face fabric that can cut the wind, making it a great option for alpine adventures. While the Patagonia Thermal Weight is one of the warmest synthetic options we've found, it still doesn't match the relative warmth of thicker Merino wool base layers.
Breathability and drying speed work together to ensure your skin stays dry, whether you're pushing the aerobic threshold or merely hanging out. 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. After our sweaty runs, we look at the fabric to see if moisture is retained in its fibers or if it's as dry as a bone.
It's not surprising that the fastest base layer bottoms to dry are those that are the thinnest. The thinner materials allow air to pass through more readily, thus allowing evaporation. The best breathers of the group are the Icebreaker 260 Zone Leggings, Odlo Performance Light, and Smartwool Merino 150. These are all a good choice for trail running or backcountry ski missions. We prefer the Icebreaker 260 Zone when the temperature is decidedly "cold" (near to below freezing) and the Odlo Performance Light for cool to cold weather (40s to 60 degrees Fahrenheit). Both of these models, unlike the Smartwool Merino 150, have special ventilation zones that target areas of the lower body that heat up and sweat the most (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 Kari Traa Rulle, which offers a softer and more relaxed structure. Synthetic fabrics are typically more porous too. On the trail, the Patagonia Capilene Midweight is the fastest to dry with its thinner, rigid, and porous construction.
Both Patagonia Capilene models actually show a similar drying speed. Even though the Patagonia Capilene Thermal Weight has more material and absorbs more water, it's able to 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 250 and Meriwool Merino 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 is also going to offer the highest level of comfort throughout the entire day of adventure. So, we take the time to evaluate comfort and fit. Fit is not scored, as it is a subjective variable. To test, we put each bottom on, wear it all day, and record our experience with each base layer. We chill out, we sweat, we drink coffee, and even sing a few songs. 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 Icebreaker 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 sleep. We love that the designers at Icebreaker gave these leggings a little bit of lycra 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 Merino 250 bottoms are also quite comfortable. While these bottoms are thick enough to keep you warm and provide enough coverage to be worn on their own, 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. Other lighter merino wool bottoms like the Icebreaker Oasis are also super comfortable and have a softer feel next to the skin.
Other synthetic contenders feel quite good as well; however, they're typically just not as comfortable and cozy. That is until we tested the Kari Traa Rulle High Waist Pant which offers a stylish and modern design that hugs our curves and feels silky soft next to our skin. We love the high waistband that keeps these bottoms in place during activity.
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 Odlo Performance Light Bottoms the most but love the affordable features of the Kari Traa Rulle High Waist Pant. 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 piece tested so far is the Patagonia Capilene (100% polyester) option. 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.
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 oz., 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 Icebreaker Merino 260 Zone Leggings, tend to hold up to wear and tear much better than their 100% merino wool competitors.
Others with a thicker construction are seemingly more durable than those that are thinner. However, we've found that these thicker contenders actually snag more easily and pill faster than thinner options. Of the merino wool bottoms made only with this fabric, the Icebreaker Oasis proves to be the best. The material is tightly knit, and even for its thinner construction, it seems super burly. A great addition when considering increased durability over time.
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 on your quest for the perfect base layer and that you stay warm and dry throughout the colder months of the year.
Looking for the best women's winter jacket? We've...
Ad-free. Influence-free. Powered by Testing.
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.