Best Long Underwear for Women of 2020
Best Overall Long Underwear Bottoms
Smartwool Merino 250 Bottoms - Women's
The SmartWool Merino 250 Bottom is our favorite for its thick and comfortable 100% merino wool fabrics that provide ample warmth while keeping you dry. This pant offers the widest range of thermoregulation and comfort while traveling from cool to cold climates. It's stacked with 250-grams of naturally odor-resistant merino wool fibers that'll still perform even if you're on day 10 of a backpacking mission, with no washes in between. All these excellent features, in addition to a versatile fit, makes this piece a favorite long underwear bottom that we enjoy wearing all over the world.
Our only caveat lives with its durability. Since the fabric is so soft, it can catch easily on sharp surfaces, and small holes can appear. Snuggle up with a good book, or hit the hills with this fantastically warm and cozy option that's continued to be a favorite for years.
Read review: SmartWool Merino 250 Bottom - Women's
Best Bang for Your Buck
Patagonia Capilene Midweight Bottoms - Women's
Notorious for its durable design, the Patagonia Capilene Midweight once again rises to the top for performance and value. Constructed of 100% recycled polyester, this pant has a midweight construction, versatile enough to wear during all four seasons. The smooth-face fabric retains its shape while thermoregulating efficiently. It's thin, easy to layer, and boasts all-day comfort. The synthetic material provides superior durability with wicking power that's hard to compare. Sport the latest patterns and colors - there are many to choose from.
Unfortunately, synthetic materials simply aren't as cozy as merino wool. The fabric (despite its treatment) does get smelly after a few days of use, so it's not our top choice for multi-day missions. If you seek a highly durable option that won't drain your wallet, this synthetic contender is one to take a look at.
Read review: Patagonia Capilene Midweight Bottom - Women's
Best Bargain for Merino Wool
Meriwool Merino Thermal Pants - Women's
The Meriwool Merino Thermal Pant for a woman is heralded as a value pick by our female testing team. Built with 100% merino wool, it offers a similar range of thermoregulator as much more expensive options at an affordable price. We appreciate the great color choices, soft fabrics, and superior wicking power that have kept us dry during our testing period. The fabrics dry quickly and insulate, even when wet. This is a great choice for cold winter days under a pair of pants, and keeps the chill away on cold ski lifts.
With a lower price comes a step down in durability. While the materials seem to hold up well, the fit did stretch out during our use period. Its overall design is noticeably less refined compared to elite bottoms, like the SmartWool Merino 250. But, this Meriwool pair allows you to benefit from the advantages of merino wool fabric at a much more accessible price point.
Read review: Meriwool Merino Thermal Pants - Women's
Best Fleece-Lined Synthetic Option
Arc'teryx Rho LT Bottoms - Women's
Over the years, the Arc'teryx Rho LT has become a versatile favorite. We are absolutely in love with its 100% synthetic construction that doesn't stretch out. What's more, is the super cozy Torrent fleece that feels soft against the skin and provides superior wicking performance. The thickness is just right, with fantastic breathability and supreme durability. With a long length and super stretchy fabrics, it's built to fit all shapes and sizes, with fun color choices. While it's marketed as a pair of lightweight bottoms, it's definitely thicker than our definition of "lightweight." We find it better suited for colder weather when paired with a snow pant. It is one of the most versatile synthetic competitors out there with a cozy fleece lining.
The only downside to this bottom is the price and the fact that it easily absorbs water. The upside is that it dries quickly, and after nearly two years of hard use, the fabrics still look great. If you're looking for a super cute durable base layer bottom for cold weather that can be used for all seasons, this is the one to invest it.
Read review: Arc'teryx Rho LT Bottoms - Women's
Best for Lightweight Performance
Ortovox Rock'N'Wool Pant - Women's
Over the last year, we've been testing the Ortovox 185 Rock 'N' Wool Pants during warmer spring days, cool autumn nights, and throughout winter. This contender tends to be the go-to when we need some coverage when running or a layer to stack under a thin pair of snow pants for backcountry skiing. The 100% merino wool construction is warm enough to keep you insulted through the winter months and features superior breathability. The fibers are long, grabbing moisture from the skin and moving it to keep you dry in all conditions. If you prefer a thin long underwear bottom, this is our top recommendation.
Being of thinner material, these bottoms are not the warmest we tested. If you want a base layer to keep you warm in winter during periods of inactivity, we recommend looking elsewhere. We had some initial durability worries, but it's still going strong after over a year of full testing. When wearing it on its own, we observe a couple of places where the material has snagged, but no other issues. For active aerobic sports, this is the bottom that we'd recommend throughout all four seasons.
Read Review: Ortovox Rock'N'Wool Pant - Women's
Why You Should Trust Us
Amber King is an outdoor educator, adventurer, and gear tester. While she's climbing, snowboarding, hiking, sailing, and trail running, she's commonly wearing a great pair of base layer bottoms to keep her warm and comfortable on all adventures. She's tested them throughout the far reaches of the world. From sailing in the rainy climates of the Faroe Islands to trail running around the Cordillera Huay Huash in Peru. When she's not exploring, you can find her working on her non-profit that provides outdoor learning experiences for kids. She works outdoors every day for hours in all weather, making her a great tester of this apparel.
When testing long underwear bottoms, we consider different ways each bottom can be used. We take stock of what's on the market, selecting the highest rated products with the best reputation. Then, we test each product side-by-side after we buy each at retail price. We've tested long underwear bottom for over three years, allowing us to test across a range of conditions. We've taken each model on international trips—sailing on the North Seas, running in Icelands, and used each locally while climbing, biking, and exploring. Colorado, Amber's hometown, is known for hourly shifts in its weather, making it a great testing site. After our field tests, we assess each product, score it, and tell you all about our findings and thoughts.
Analysis and Test Results
A solid long underwear bottom is a key part of any woman's outdoor wardrobe. Designed to sit next to the skin, it wicks away moisture to keep your skin dry. While each bottom can be used on its own in warm weather, it is typically used in a layered system during the winter. We look at a range of base layer bottoms in a variety of weights. Testing each side-by-side, we evaluate each product using four key metrics, including 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 REI Midweight Bottoms offer the lowest price, this synthetic base layer bottom is super thin and doesn't have the same level of warmth and durability as other thicker products, which most folks want in this category. The Patagonia Capilene Midweight is the top dog when it comes to excellent performance overall for the price. However, it's a synthetic pair of bottoms, which isn't as warm as merino wool. High-value merino wool options include the Meriwool Merino Thermal Pant and REI Co-op Merino Bottoms. The Meriwool Merino is warmer with a wider range of thermoregulation, while the REI Co-op model holds its shape a little better during activity.
The insulative warmth of a base layer bottom balances with breathability to provide great thermoregulation. When looking at warmth, know that most models come 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 when they actually are 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 what we think the effective fabric weight of each model is.
During our testing period, we perform a few tests. First, we observe the fabrics and make-up of each product. We look at the fabric weave to see how tight or loose it might be, and its relative thickness. Then, we test warmth by playing and working in cold weather. For example, adventuring on a boat on the North Seas or sleeping under the stars on frosty nights. We carry our layers with us, cycling them out to see which offers the best insulative warmth on their own and underneath a pair of pants. We then take notes, compare, and report back to you.
Through extensive testing, we learned that the natural organic fibers of merino wool don't just feel amazing against the skin, but offers the best range of thermoregulation and warmth for the coldest days of the year. Merino wool base layer bottoms, like the Meriwool Merino Thermal and Smartwool Merino 250, offer the most warmth with its thicker fabrics that wick moisture and insulate very well on cold days.
Merino layers with a little less insulation like the Icebreaker Oasis and the Ortovox Rock 'N' Wool, both wick a little better than the thicker options and have a thinner construction. Even though the Icebreaker Oasis has 200 g/m² of merino fabric, it feels much lighter than the Smartwool 250 or the REI Merino Midweight Pants (200 g/m²). It's still very warm and insulates in for cold weather, but aren't our main choices for the coldest days out there. The Ortovox Rock 'N' Wool (185 g/m²) is the thinnest 100% merino wool pant making it a top choice for those seeking a lightweight construction.
While synthetic long underwear bottoms do great work 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 is a pretty warm option loaded with a polyester-spandex construction. It is warmer than the Patagonia Capilene Midweight bottoms, given its thicker fabrics and a higher insulation level. While this bottom is warm with wear, it feels a little cold getting into, especially on cold mornings. The Arc'teryx Rho LT is advertised as a lightweight bottom but actually feels like it has the same amount of thickness as the Capilene Thermal Weight and is pretty insulative.
What's unique about the Arc'teryx Rho LT pant is the super cozy fleece lining that offers added warmth. Both the Patagonia Thermal and Arc'teryx Rho Lt pants can be worn on their own during the cool weather of the summer. The Patagonia Thermal Weight has a thicker face fabric that can cut the wind, making it a great option for alpine adventures. The Arc'teryx Rho LT is also protective but uses a super cozy fleece lining on the interior. Both have great warmth when worn on their own and under a pair of pants. These are both the warmest synthetic options we've found but still don't match the relative warmth of thicker merino wool products.
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, and hiking in warm 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 breather of the groups is the Ortovox Rock'N'Wool and Smartwool Merino 150. The Smartwool 150 is not as comfortable as the Ortovox Rock'N'Roll, but both are a good choice for trail running or backcountry ski missions. We prefer the Ortovox because the fabrics have a looser weave, are more comfortable, and offer a little more warmth when it's cold outside. We also think it breathes just a hair better than the Smartwool Merino 150, being just as thin but more porous.
Following in breathability are the synthetic competitors. Synthetic fabrics are known for their rigid structure that typically wicks well and dries quickly. Synthetic fabrics are typically more porous too. On the trail, the Patagonia Capilene Midweight is the fastest to dry with its thinner construction. The REI Midweight has a similar drying speed, with a design that is a touch thinner but with a fabric knit that is tighter than the Patagonia Capilene Midweight.
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.
Of the thinner wool contenders, the Ortovox Rock 'N' Wool and REI Merino Midweight have a similar performance level. The REI Merino has a slightly heavier construction, making ita touch less breathable. The Ortovox Rock 'N' Wool and Icebreaker Oasis are also similar here. Both have a looser weave in the fabrics, with the Ortovox showing less material per meter squared. Overall, the Ortovox Rock N Wool has superior wicking power and breathes very well of the merino wool options.
Thicker base layers like the Smartwool 250, Meriwool Merino and Arc'teryx Rho LT 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, moisture can accumulate in the fabrics. When this happens, the wool contenders typically do better as wool can retain heat when wet better than synthetic fabrics. That said, with adequate ventilation, both are built to breathe well.
Comfort and Fit
A long underwear bottom that'll feel cozy from the hill to your bed is the best you can find. One that fits right is also going to be comfortable all day while adventuring. 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 compare each. We chill out, we sweat, we drink coffee, and even sing a few songs. We determine which feels great against the skin, which starts to lose their shape, and which simply need to be sized up or down.
Soft, cozy, roasty, and toasty. The Arc'teryx Rho Lt Bottom is by far one of the best when it comes to next to skin comfort. While most synthetics fabrics can feel stiff, the Torrent fleece is super soft for all-day wear. Against the skin is an actual fleece layer, which no other base layer can compete. With its stretchy fit, it's by far one of the most comfortable base layers we've ever tested. We love that the style is versatile enough to wear on its own or underneath a pair of pants.
The Smartwool Merino 250 bottoms are also quite comfortable. While you can wear it on its own, the fabric sags eventually and doesn't look as good as the Arc'teryx Rho LT on its own. 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 REI Merino Midweight, Icebreaker Oasis, and Ortovox Rock 'N' Wool are also super comfortable. Of them, the Ortovox Rock 'N' Wool has the softest material on the skin, though it's also the thinnest.
While fleece-lined synthetics and wool contenders are pretty darn cozy, other synthetic contenders feel good as well, but they're not as comfortable. Since the fibers are 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 bottoms the most. The thinner fabrics are soft against the skin, similar to the REI Midweight, but feel a tad warmer.
The Patagonia Capilene Thermal Weight is comfortable, but the fabrics feel stiffer with a more abrasive waistband. The REI Midweight is quite thin and gets cold easily. The Smartwool Merino 150 has a very rigid fit that doesn't stretch much. This is the only pant that we recommend sizing up in if you're looking for a merino-synthetic blend that won't sag or stretch during use.
Durability is key when buying a high-value product. You don't want to invest in a pair of bottoms only to find out that they fray and wear out after a few uses. When layered underneath other layers, the fabrics need to be durable as they will be exposed to high friction environments.
To test durability, we observe wear and tear after our testing period and continue to test until a new iteration of the product is developed. We hike, ski, climb and run with each, both layered and on its 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 Arc'teryx Rho Lt (84% polyester, 16% elastane) and the Patagonia Capilene (100% polyester) options. We've tested each for two years, with each looking great after hundreds of miles and hard use on the trail.
Of them all, the Arc'teryx Rho LT impresses us as the most durable. There are some seams showing a little unraveling, but this is after multiple years of running, hiking, and sliding through slot canyons. The Capilene options are doing great too; however, the Midweight isn't performing as well as the Thermal weight. This isn't surprising as the Thermal weight is much thicker.
While merino wool isn't as durable as synthetic fibers, it's not like they will fall apart easily. Bottoms that integrate both merino wool and synthetic fibers into the construction, like the Smartwool Merino 150, tend to hold up to wear and tear better than 100% wool bottoms.
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. The Ortovox Rock n' Wool is close behind, even featuring thicker fabric reinforcements in the knees, a high wear area. A great addition for added 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 sit best next to your skin. We hope our in-depth research has helped you in this quest and that you stay warm throughout the cool and cold months.
— Amber King