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Our backcountry clothing experts have tested close to 40 pairs of the best long underwear for women over the last 8 years, with the top 14 in this review. Each next-to-skin layer has seen 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.
Weight: 4.90 oz | Material: 92% recycled polyester, 8% spandex
REASONS TO BUY
Supersoft Polartec fabric
Great fit enhances mobility
REASONS TO AVOID
Fabric holds odor
Known for its amazing wicking power and breathability, the Patagonia Capilene Thermal Weight rises to the top for synthetic performance. Constructed of 92% recycled polyester and 8% spandex, this pant (though marketed as a thermal weight) has more of a midweight construction that provides optimal performance throughout most of the year. The see-through design allows air to penetrate the fabric, and the subsequent wicking power is hard to beat. While synthetics aren't typically known for their next-to-skin comfort, we love how the Polartec power grid fleece feels against the skin, in addition to the stretchy fit that moves with our body.
Unfortunately, despite the odor control treatment, these bottoms get smelly after only a few days of use, so they aren't our first choice for multi-day backcountry missions. The Capilene Thermal is admittedly a bit more niche — they aren't your "hang around at camp lounge pants." However, they dry quickly, excelling at technical, high-output pursuits. If you are seeking a highly breathable synthetic pair of long underwear that doesn't skimp on comfort and fit, these will not disappoint.
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.
Weight: 6.40 oz | Material: 92% polyester, 8% spandex
REASONS TO BUY
Cute and fitted style
Easy to wear on their own
Smooth, silky, and stretchy fabric
REASONS TO AVOID
Fabric absorbs and holds moisture
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 began. All complaints aside, these synthetic tights impressed our testers with a competitive performance, especially considering the modest price tag.
Weight: 4.80 oz | Material: 84% polyester/16% elastane
REASONS TO BUY
Great fit and waistband
Soft synthetic fabric
Bonus stash pocket on thigh
REASONS TO AVOID
Merrow stitch seams accumulate fuzz from friction
The Arc'teryx Rho Lightweight Bottom is a super light, versatile, and high-performing long underwear bottom that features some of the most comfortable, internally brushed synthetic fabric along with a great fit. We love the high-rise, thick waistband that is not only flattering but functional, in addition to the slim fit that aids in offloading moisture from the minimalist design. These were some of the only bottoms that we tested that feature a stash pocket on the thigh, which is great for storing energy gels, a couple of keys, or a phone.
This versatile design provides enough warmth and modesty to be worn on its own for trail runs in the spring and fall or when layered beneath your favorite ski bibs for added insulation throughout the winter. The Rho is a bit pricey compared to other lightweight synthetic options in this review, and the merrow stitching — similar to a welded seam — gets fuzzy when encountering velcro or a lot of friction from additional layers. Still, the Rho is high performing and highly versatile, the perfect layer for running, skiing, or yoga.
The Smartwool Intraknit Thermal Merino Bottom quickly became our favorite pair of long underwear geared to optimize cold weather performance. The fabric blend utilizes the odor-free benefits of Merino along with the durability of polyester. But what really sets these bottoms apart from the rest is their gender-specific pattern articulation and unique ventilation panels that increase breathability throughout the design while capturing warmth generated during activity.
While we are truly impressed by the ability of the Intraknit to keep us warm when moving in frigid temperatures, this design is not without some caveats. The overall thicker fabric not only increases bulk when layering but it also reduces the drying speed. And while we love the 2" waistband for the way it hugs our curves and keeps these bottoms in place, the waistband was typically the only portion of these bottoms that would trap moisture. Those things aside, if you're looking for long underwear bottoms with a more substantial and warmer weight but that still perform well during high-output cold weather activities, this is the layer for you.
Lightweight material can tear if you're not careful
The Odlo Performance Light Bottoms are the lightest pair of long underwear bottoms that we tested. This pant is built for picking up the pace in cool weather, featuring synthetic materials with ventilation panels throughout the length of the legging to offer superior wicking ability and thermoregulation. Because the material is ultralight, we recommend this layer to provide extra warmth during trail runs at the change of season or layered below pants for Nordic skis during the winter months.
We're proud to report that even after two years of testing, we've experienced no durability issues with these bottoms. 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, aid in moisture management, 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 six key metrics:
Warmth (25% of overall score weighting)
Breathability (20% weighting)
Comfort and Fit (20% weighting)
Durability (15% weighting)
Drying Speed (10% weighting)
Layering Ability (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, 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 in the Eastern Sierra. 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.
We refer to the Patagonia Capilene Midweight as our synthetic workhorse, followed closely by the Odlo Performance Light Bottoms — and both come in at a reasonable price. We were 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 and cozy as Merino wool.
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 evaluating warmth, you should first consider that most models are available in a variety of different 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 one weight and perform more like another. To help you navigate confusing marketing claims, we provide side-by-side comparisons and let you know our opinion regarding the effective fabric weight offered by each pair of long underwear bottoms.
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 is best for you prior to making your final decision.
During our testing period, we began by observing the fabrics and their construction, assessing the tightness and relative thickness of the weave. Then, we test warmth by playing and working in cold, inclement 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 not only feel amazing against the skin, but typically offer the best range of thermoregulation and warmth for the coldest days of the year. Merino wool base layer bottoms, like the Ridge Inversion and the Meriwool Merino 250 Bottom, offer the most warmth due to thicker fabrics that insulate very well on cold days.
If you dig the ventilation panels and optimized breathability, the Smartwool Intraknit Thermal Merino Bottom has a blend of Merino wool and polyester. And while fully synthetic options aren't typically as warm as wool or wool blends, some contenders like the Patagonia Capilene Thermal Weight are closing that gap. Both of these bottoms offer a modern perspective on thermal insulation, increasing the overall warmth of the layer by increasing its ability to offload moisture. We recommend these performance bottoms for high output warmth during cold weather activity, but if you're looking for the warmest model for more sedentary activities or riding the chairlift, stick with the Ridge Inversion.
The Patagonia Capilene Midweight Bottoms feature a 100% recycled polyester construction that we consider our cold weather workhorse. 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 high-intensity activities during the cooler months of the year or when layered underneath insulated pants for Nordic skiing.
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 backcountry skiing, hiking, climbing, and running in both warm and cold weather conditions. Finally, we evaluate the fabric to see if any moisture is retained within the fibers or if it's able to stay dry as a bone.
It's not surprising that the most breathable long underwear bottoms are often the thinnest. Thinner, see-through materials allow air to pass through more readily, thus facilitating optimal evaporation. Some of the most breathable layers in this review are the Patagonia Capilene Thermal Weight and Odlo Performance Light. Since the Thermal Weight is rather see-through, we don't recommend it as a stand-alone piece, but its lightweight design performs incredibly well in a layered system or with spandex bike shorts underneath. We prefer the Smartwool Intraknit for backcountry skiing or winter training runs when the temperature is decidedly cold (near to below freezing) and the Odlo Performance Light for cooler weather (40 to 60 degrees Fahrenheit). The Thermal Weight, Intraknit, and Odlo receive higher scores because they have special ventilation zones that target specific areas of the lower body which are prone to absorbing body heat and sweat. These body-mapped ventilation panels work well to promote airflow in these areas, offloading moisture while maintaining body heat.
Synthetic fabrics are often known for their rigid structure. An exception to this rule is the Arc'teryx Rho Lightweight. This layer quickly became a go-to for spring training runs and backcountry skiing due to the ability of the soft, brushed Torrent fabric to wick and shed moisture. Another design that offers less rigidity is the REI Co-op Midweight, but it unfortunately didn't breathe as well as its ventilated competitors, often retaining sweat in the waistband and requiring more time to dry fully. While synthetic fabrics are typically more porous than wool, the Midweight features a tightly woven and slim-fitting polyester fabric. On the trail, we prefer synthetics such as the Rho, which features a lighter-weight construction.
Long underwear bottoms like the Ridge Inversion, the Smartwool Classic Thermal, and the Meriwool Merino 250 are simply much thicker in construction and not exactly known for their breathability. When we layered these bottoms underneath another pair of pants, we noticed that they lacked the ability to wick moisture away from the body, often resulting in sweat accumulating in the fabric, which can get cold quickly. Throughout testing, we observed that the wool contenders typically perform best when sweaty because wool can retain heat, even when wet, much better than thicker synthetic fabrics. 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 hope for. Bottoms that fit correctly should also offer the highest level of comfort throughout an entire day of adventures. To test this metric, we put each bottom on, wore it all day, and recorded our experience.
The Smartwool Classic Thermal are 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 curves. Like many other Merino wool contenders, these are 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 Short Pants are also super comfortable and have a softer feel next to the skin, thanks to their 100% Merino wool fabric.
Synthetic bottoms often feature fibers that are hollow, which can result in a less comfortable feeling next to the skin. Still, we noticed a couple of options that prove this theory obsolete. The Arc'teryx Rho Lightweight and the Patagonia Thermal Weight feature, respectively, a brushed interior or Polartec fleece that's highly comfortable in addition to their superior, high-waisted fits. And, though not the warmest or most comfortable fabric in this review, the Odlo Performance Light Bottoms feature a great fit that is true to size and is soft against the skin, making them a great choice during cool weather activities.
We understand that durability is key when purchasing a layer essential for your winter kit. You don't want to invest in a pair of bottoms only to find out that they fray, rip, and wear out after only a few uses. In order to measure overall durability, we observe wear and tear throughout our testing period until a new iteration of the product is developed and included in the lineup. We ski, climb, and trail run in each pair of long underwear and record our experiences while layered underneath 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 skinning uphill underneath snow pants, we get a good idea of the durability each layer has to offer. We continue to update this section throughout the year as we gather more information.
If the most durable bottom out there is what you prefer, look for thick fabrics made from synthetic materials. These strong fibers are often stiffer and more rigid, thereby providing better resistance to abrasion and stretch when compared to their Merino wool competitors. The most durable layer we've tested so far is the Patagonia Capilene Midweight. We've tested these bottoms for years and are happy to report they still look great after hundreds of miles and intense use on the trails. Both the Midweight and Patagonia Capilene Thermal Weight offer a durable elastic waistband and flatlock seams, which inspire confidence in their construction — if only the odor treatment was as effective because these layers often smell after minimal use.
We were perhaps the most curious as to how the Patagonia Thermal Weight and the Odlo Performance Light Bottoms would hold up during intense activity due to their see-through or ultra-thin designs. We are pleased to report that we have experienced no durability issues thus far, though the fabric is some of the thinnest that we tested, and we therefore can't imagine it will last as long as a thicker and more rigid synthetic design.
Another impressive bottom is the Arc'teryx Rho Lightweight Bottom, which features a high-quality merrow stitch similar to a welded seam. The only issue that we noticed with these bottoms was the tendency for the seams to get a little fuzzy if there was friction between the bottom and our ski bibs; otherwise, they were with us for many training miles without issue.
A thicker construction is seemingly more durable than a thin one. However, thicker contenders can also snag more easily and pill faster than thinner options. Of the 100% Merino wool bottoms, the Icebreaker 200 Oasis is notable here. The material is tightly knit, and it seems super burly even for its thinner construction. The Kari Traa Rose High Waist features a durable, thick, and well-made design reinforced with flatlock seams. Another impressive 100% Merino wool design is the Ridge Inversion, which has held up to rigorous use well. Bottoms that integrate both Merino wool and synthetic fibers into their construction, such as the Smartwool Intraknit, also tend to hold up to wear and tear much better than their 100% Merino wool competitors.
Measuring the overall drying speed for each layer was an important undertaking for us. For each pair of long underwear, we simulated what it would be like to soak and dry each layer while in the backcountry for an extended period of time.
Our results revealed that the synthetic fabrics that feature a lightweight construction typically offer the fastest drying speeds, while the Merino Wool layers typically require a much longer amount of time to dry completely.
As always, we love when a long underwear bottom outperforms our expectations, so we're happy to report that the Patagonia Capilene Midweight Bottom, though considered a midweight fabric, offered the fastest drying speed by a long shot, drying in only 32 minutes.
Other synthetic options that offer fast drying speeds include the Patagonia Thermal Weight, the Arc'teryx Rho, and the Odlo Performance Light, drying in less than 45 minutes.
Though most midweight Merino wool bottoms took longer to dry due to a thicker construction devoid of the porous structure of their synthetic competition, there were a few that stood apart from the rest. The Smartwool Classic All-Season Merino Bottom is notable here, as are the Icebreaker 200 Oasis Leggings. Of the thickest Merino wool bottoms, we suspect that the polyester blend aids in the faster drying speed for the Smartwool Classic All-Season and Smartwool Intraknit.
There is a lot to consider when evaluating the layering ability of each base layer. We tried to assemble a variety of different cold weather kits to determine which long underwear bottom performed best within a layered system. Whether layering underneath the grippy inner fabric of our favorite ski bibs or below the smooth interface of our puffy and rain pants, we gave the highest scores to the layers that required the least amount of adjustment, had the smoothest fabric, and promoted mobility rather than limiting our range of motion.
The Merino wool bottoms at the top of our list include the Icebreaker 200 Oasis and the 3/4 length design of the Ortovox 185 Rock'N'Wool Short Pants. We love the Icebreaker Oasis for its smooth wool fabric and low profile elastic waistband, though we did notice some piling from some friction after skinning uphill. The Rock'N'Wool Short Pants offer the least amount of bulk in any layered system that we assembled due to their 3/4 length, which rests just below the knee, leaving just enough extra room for tucking beneath the very top of our ski socks. We appreciated the Short Pant design when the temperatures heated up during our spring skiing season, leaving more room in our ski boots and less material to absorb moisture when moving quickly uphill.
Our top-performing synthetic options include the Odlo Performance Light, REI Lightweight Base Layer Tights, and the Patagonia Capilene Midweight. The Odlo and REI options feature super low profiles and ultralight fabrics, which took up the least amount of space in our ski bibs, in addition to a very smooth interface between our puffy and rain pants. We love these options for spring skiing and appreciate the extra room for increased airflow and range of motion when pursuing backcountry ski objectives. The higher waist and smooth 100% polyester fabric increase the glide between additional layers over the top, and we love that the waistband, though double-banded, sits above our natural waistline and reduces bulk, allowing other layers to lay flat against the skin.
Another notable option is the Smartwool Classic All-Season Merino Bottom, which didn't impress us with durability, but the superlight fabric almost feels like you have nothing on beneath your ski bibs. The Merino wool design also has a touch of nylon which we suspect allows for a better interface with additional layers. A bit of a surprise in this category was the Ridge Inversion, which features a stripped-down classic design and a higher waist that may take up a little more room than a lightweight option, though it never reduced our mobility, especially considering it is the only heavyweight option in this review.
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.
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.