Best Long Underwear for Women of 2024

Women's Base layer bottoms and thermal underwear bottoms to stay warm in cool weather

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Published April 26th, 2024

woman on top of mt st helens wearing baselayer bottoms

Cold weather activities can quickly jump from Type I to Type III fun if your body gets cold!  Good long underwear is key to being comfortable when pursuing outdoor activities when the temperatures drop. Long underwear and baselayer bottoms should provide warmth, wick sweat and breathe well to manage moisture, allow full range of motion, closely hug your body without slipping, and fit under other layers

After hours researching options and poring over customer reviews, I narrowed down the 9 best women's base layer bottoms to test including merino wool and synthetic options. The long underwear I considered ranged from lightweight to heavyweight in warmth. 

I'm a former President of the American Long Distance Hiking Association-West, mountaineer, packrafter, snowshoer, and backcountry skier. To test women's long underwear bottoms, I wore them on all kinds of winter outings ranging from snowshoeing, backpacking, hiking, mountaineering and packrafting to find out which performed best in different conditions and activities. These are the best women's long underwear–as tested on adventures from climbing Mt. St. Helens to snowshoeing in Oregon to packrafting Utah. 

Looking for men's long underwear? See our Best Men's Long Underwear guide

Looking for base layer tops? See our Best Base Layers guide.


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Women’s long underwear comparison table

WOMEN'S LONG UNDERWEAR BOTTOM TREELINE AWARD MSRP* MATERIAL WARMTH WAIST SIZES WEIGHT (OZ)**
Smartwool Classic Thermal Merino Base Layer Bottom Best overall
Read why
$115 Wool Midweight Mid XS-XL, 1X-4X in extended sizes 7.5
Arc'teryx Rho Best synthetic
Read why
$100 Synthetic Lightweight High XXS-XXL 5.3
Mons Royale Best lightweight
Read why
$120 Wool Lightweight Mid XS-XL 4.9
Arc'teryx Rho Heavyweight Best heavyweight
Read why
$120 Synthetic Heavyweight High XXS-XXL 8.1
Ridge Merino Inversion Best affordable
Read why
$80 Wool Midweight Mid XS-XL 7.3
Icebreaker 260 Tech Mid Rise Best hiking
Read why
$125 Wool Midweight Mid XS-XL 7.3
Icebreaker 200 Oasis $105 Wool Lightweight Mid XS-XL (REI also has 2x and 3x?) 6
Smartwool Intraknit $130 Hybrid Mid to Heavy Mid XS-XL 9.3
Arc'teryx Rho Merino Wool $120 Wool Midweight High XXS-XXL 7
REI Midweight Base Layer tights $54.95 Synthetic Midweight Mid XS-3X, Petities: XS-XL 6.7
REI Merino 185 Base Layer Bottoms $79.95 Wool Lightweight Mid XS-XL 5.6
REI Lightweight Base Layer Tights $39.95 Synthetic Lightweight Mid XS-XL 5.8
Patagonia Capilene Midweight $79.00 Synthetic Midweight Mid XXS-XXL 5.5
Helly Hansen Lifa $100.00 Hybrid Midweight Mid XS-XL 10.5
Icebreaker 3/4 length 95 Wool Midweight Mid XS-XL 7.8
SOURCE: Manufacturers

* We often find these available below MSRP. See our Deals Page for more info.

**Weights measured on our scale.



The winners

Smartwool Classic Thermal Merino Base Layer Bottom

Material: 100% Merino wool 
Available sizes: XS-XL, also available in plus sizes 1X-4X
Waist: Mid-rise
Weight: Midweight, 250g/m2
Garment weight (size M): 7.5oz
What we liked: Soft fabric, wide waistband without any digging, huge range colors and patterns, extended sizing
What we didn’t like: No crotch gusset

We think the Smartwool Women’s Classic Thermal Merino Base Layer Bottom is the all-around best long underwear choice for most people and activities. The moment I first tried these on, I knew they would be a favorite. The fabric is super soft on the skin with no itchiness from the start, which is extra impressive because the fabric is 100% merino — no synthetic blend!  

What really makes the Smartwool Classic Thermal Base Layer Bottom stand apart from other base layer bottoms is the waistband construction. Instead of relying on a separate elastic band sewn on top, which tends to dig into the skin and create uncomfortable pinch points, the Smartwool Classics encase the elastic in the same merino fabric as the rest of the bottoms. This construction helps distribute the pressure evenly and create a secure fit without feeling constricting.

Compare prices of the Smartwool Classic Thermal Merino Base Layer Bottom

Smartwool Classic Thermal Merino Base Layer Bottom

I tested this base layer in a variety of outdoor activities, including one memorable snowshoe trip in the dark to a remote cabin when it was 33F and pouring rain the entire time. The Smartwool Classic bottoms kept me warm and dry under my rain shell — no clamminess at all.  Because they are so cozy and comfortable, I also find myself wearing them simply to lounge around the house. The fabric is sturdy and durable, and while I always try to be careful with my merino garments, I don’t feel the need to baby these Smartwool bottoms. They have held up beautifully to regular use.  

Smartwool Classic Thermal Merino Base Layer Bottom

The only feature I would’ve liked to see in these bottoms that is missing is a fully gusseted crotch for a little more range of motion. However, I found the more minimal diamond crotch and flatlock seams to be quite comfortable, and the inherent stretch of the merino knit allows good mobility.

Smartwool Classic Thermal Merino Base Layer Bottom

The Smartwool Classics are available in a multitude of fun colors and patterns, as well as classic solids. Additionally, these base layer bottoms are available in the widest range of sizes of any of the base layer bottoms we tested, XS through 4X.  

Customer reviews echo all the same reasons we praise the Smartwool Classic bottoms: the soft and cozy fabric, toasty warmth and breathability, and great fit.


Best synthetic long underwear: Arc’teryx Rho Bottoms 

Arc'teryx Rho Bottoms

Material: Synthetic - Torrent™ 190 with Polygiene®- 84% polyester, 16% elastane
Available sizes: XXS - XXL
Waist: High-rise
Weight: Lightweight
Garment weight (size M): 5.3oz
 What we liked: Durable fabric, quick drying, excellent fit
What we didn’t like: Pocket too small for most phones. 

The Arc'teryx Rho Bottoms are our winner for best synthetic women's long underwear. The Arc’teryx Rho Bottoms have the most intricate patterning of all the base layers we tested, and it shows. The fit is superior as well as stylish. The wide paneled waistband covers a narrower elastic band that keeps the bottoms from falling down. A fully gusseted crotch makes for chafe-free movement, and seaming below the knees keep the fit dialed in throughout the entire length of the legs. 

Compare prices of the Arc’teryx Rho Bottoms

Arc'teryx Rho Bottoms

The synthetic fabric also has a smooth feel on the outer face and layers glide over the fabric easily. The high elastane content of the fabric makes the Arc’teryx Rho Bottoms very stretchy, fitting a variety of body shapes well. We had several testers wear these long underwear bottoms–from people with curvy, muscular thighs and bottoms to more narrower legged people. In each case, we were surprised by how well the same pair of size medium long underwear bottoms fit such different shaped bodies.

Arc'teryx Rho Bottoms

These bottoms not only serve as a great layering piece, but provide enough modesty that they can easily be worn by themselves as leggings. The fabric is opaque, the seaming is very sleek, and there’s even a zippered pocket on the right thigh that fits a credit card, cash, or keys. Unfortunately, the pocket is a bit too small for most cell phones. 

Arc'teryx Rho Bottoms

I found myself regularly grabbing the Arc’teryx Rho bottoms for quick hikes in Forest Park, my local trail system. Because they were one of the few pairs of long underwear we tested that were modest enough to wear by themselves, they’re so convenient to wear for shoulder season days where the mornings start out cold. I could easily throw a pair of hiking pants over the Rhos, and then when temps warmed up, I could take off the pants and just wear the Rhos. This system was much easier than removing the inner layer, as I would've had to do with most other long underwear bottoms! 


Best lightweight long underwear: Mons Royale Cascade Merino Flex Legging

Mons Royale Cascade Merino Flex Legging

Material: blend 81% merino, 12% nylon, 7% elastane
Available sizes: XS-XL
Waist: High-rise
Weight: Lightweight
Garment weight: 4.9oz
What we liked: Comfy waistband, fun colors, performance of fabric blend
What we didn’t like: Not as soft as others

I was initially attracted to the Mons Royale long underwear because of the fun prints and colors, but I was pleasantly surprised to find the Cascade Flex Leggings also ended up being a comfortable and high-performing lightweight base layer. The Mons Royale Cascade Merino Flex Legging is our winner for best lightweight long underwear. At 4.9 oz, not only was it the lightest baselayer bottom we tested, but also performed well in varied conditions.

Compare prices of the Mons Royale Cascade Merino Flex Legging

Mons Royale Cascade Merino Flex Legging

The lightweight blend of 81% merino, 12% nylon, 7% elastane makes for a good balance of breathable, stretchy, and quick drying.  Upon initial try-on, the fabric felt slightly itchy, but disappeared after a few hours of wear, and remained soft on all subsequent wears. 

Mons Royale Cascade Merino Flex Legging

Despite not having any crotch gusseting or waistband paneling, the fit was good on my athletic thighs and butt, and I didn’t notice any chafing or rubbing thanks to the flatlock seams. The wide, soft elastic waistband stays in place. Of all the models we tested with a separate sewn-on elastic waistband, this was the most comfortable.

Mons Royale Cascade Merino Flex Legging

Testing included a spring snowshoe climb of Mt St Helens, where the Mons Royale Cascade Flex’s light weight was just right for next to skin comfort under softshells while laboring uphill in the sun, withstanding gusts at the summit, and glissading down the mountain. 


Best heavyweight Long Underwear: Arc'teryx Women’s Rho Heavyweight Bottom 

Arc'teryx Women’s Rho Heavyweight Bottom 

Material: Synthetic - Polartec® Power Stretch® Pro - 53% polyester, 38% nylon, 9% elastane
Available sizes: XXS - XXL
Waist: High-rise
Weight: Heavyweight
Garment Weight (size M): 8.1oz
 What we liked: Versatility to be worn as standalone legging, excellent fit, soft and cozy
What we didn’t like: Expensive for synthetic, pocket is too small for larger phones

The Arc’teryx Rho Heavyweight Bottoms were easily the warmest of the long underwear we tested and win our award for best heavyweight long underwear bottoms. In addition to the toasty warmth, we loved the comfort of the Arc’teryx Rho Heavyweights. The Polartec Power Stretch Pro fabric has a super soft fleece interior, making for a very cozy next to skin feel while the outer face of the fabric is a sleek and durable nylon.  

These are true multitasking bottoms. I found myself wearing them as standalone pants for everything from lounging around the house to going on a run in the snow. The Arc’teryx Rho Heavyweight bottoms have all the comfort of lounge pants but the fit and styling to make them suitable for wearing alone as leggings.

Compare prices of the Arc'teryx Women’s Rho Heavyweight Bottom 

Arc'teryx Women’s Rho Heavyweight Bottom

The fit of the Arc’teryx Rho Heavyweight bottoms is the same as the Arc’teryx Rho bottoms: it’s great on multiple body shapes thanks to the high rise fit, smartly paneled wide waistband, and the super stretchy fabric. A narrow, fully encased elastic band at the top of the waistband keeps the bottoms from slipping down. The low-profile zippered thigh pocket is handy for small items, though not big enough to fit a cell phone.

Arc'teryx Women’s Rho Heavyweight Bottom

It's worth noting that for some activities and some climates, they may actually be too warm, especially if wearing them as a layer under other pants. If you aren't sure, consider the Arc'teryx Rho we recommend above.


Best affordable long underwear: Ridge Merino Inversion

Ridge Merino Inversion

Material: 100% merino wool
Available sizes: XS-XL
Waist: High-rise
Weight: Midweight - 270g/m2
Garment weight (size M): 7.3oz
What we liked: Affordability, soft fabric
What we didn’t like: Simple construction/less dialed fit

The Ridge Merino Women's Inversion Heavyweight Merino Wool Base Layer Leggings are a great merino option at an affordable price. The 100% merino fabric is super soft, with all the benefits of wool’s warmth and breathability. 

While the construction and fit is more basic, lacking shaping panels through the waist and rear, it still has nice features like flatlock seams and a small triangle crotch panel. The elastic waistband is brushed on the inside, so it is fuzzy and soft against the skin. Some folks may appreciate the higher rise fit of the waist for extra coverage.

View the Ridge Merino Inversion

Ridge Merino Inversion

At 7.3 oz, these are one of the heavier-weight options we tested, and may be too hot for vigorous activity in all but the very coldest conditions. The Ridge Merino Inversion leggings are ideal for activities like camping, resort skiing, and snowy walks.

Ridge Merino Inversion

I used the Ridge Merino Inversion leggings on an overnight winter snowshoe cabin trip. I was dry and comfortable on an easy 3 mile snowshoe in and out, and also toasty warm while sleeping and lounging by the woodstove in the cabin.

Ridge Merino Inversion

The Ridge Merino ticked all the boxes I wanted for a luxurious feeling base layer bottom at a more affordable price than many other options.


Best hiking Long Underwear: Icebreaker 260 Tech Merino

Icebreaker 260 Tech Merino

Material: 100% Merino wool
Available sizes: XS-XL
Waist: Mid-rise
Weight: Midweight
Garment Weight (size M): 7.3oz
What we liked: Superior breathability, excellent warmth without bulk
What we didn’t like: Not the softest of fabrics against the skin, fit is more basic

The Icebreaker Women's Merino 260 Tech Thermal Leggings are our favorite choice for activities that fluctuate in intensity, such as hiking and snowshoeing. The 100% merino fabric is knit in a way that enhances breathability compared to other fabrics of a similar weight (260g/m2). The Icebreaker's merino wool is exceptional at regulating heat when powering through high intensity activities while also retaining warmth during periods of rest. 

Compare prices of the Icebreaker 260 Tech Merino

Icebreaker 260 Tech Merino

The Icebreaker Merino 260 Tech Thermal Leggings fit well thanks to a back panel yoke and crotch gusset. The mid-rise height still provides good butt coverage for my muscular bottom, and the elastic waistband is soft and doesn’t dig into the skin while still being secure.

Icebreaker 260 Tech Merino

The highly breathable fabric is soft and warm, though the feel against the skin is not quite as plush and cozy as other models. 

Icebreaker 260 Tech Merino

In addition to the garment performance, Icebreaker's commitment to sustainability is commendable, with significant strides towards eliminating plastic from their products, achieving an impressive 96% plastic-free status in 2023.

Icebreaker 260 Tech Merino

Their dedication to sourcing wool from producers that engage in regenerative practices further underscores their responsibility towards environmental stewardship.

Icebreaker 260 Tech Merino

Think hiking long underwear is too much warmth for you? Consider hiking tights instead, which often have pockets. These aren't designed for layering like a hiking base layer bottom, but can sometimes still work in cooler temperatures.


Other women’s long underwear we tested

Smartwool Intraknit Thermal Merino Base Layer Bottoms

Smartwool Intraknit Thermal Merino Base Layer Bottoms

Material: Blend 52% merino wool/45% polyester/2% elastane/1% polyamide
Available sizes: XS-XL
Waist: High-rise
Weight: Midweight
Garment weight (size M): 9.3oz
What we liked: Knit integrates shaping and ventilation without extra seams
What we didn’t like: Uncomfortable fabric feel and slim/compressive fit

Many reviewers liked the Smartwool Intraknit bottoms because they are made with a hybrid fabric and knitted-in pattern that yields great breathability and comfort. However, this knitted-in articulation was also problematic for some bodies (including mine) when the knee shaping didn’t line up with my knees. I also found the fit to feel constrictive through the thighs (I have muscular thighs from many years of Crossfit). For my body shape, the compression-like fit felt uncomfortable. Other testers and I found the ventilation panels felt itchy against the skin.

Compare prices of the Smartwool Intraknit Thermal Merino Base Layer Bottoms

Smartwool Intraknit Thermal Merino Base Layer Bottoms

Icebreaker Merino 200 Oasis Thermal Legging

Material: 100% merino
Available sizes: XS-XL
Waist: Mid-rise
Weight: Lightweight
Garment Weight (size M): 6.0oz
What we liked: Good breathability and light warmth
What we didn’t like: Not the softest fabric, fairly sheer

We tested the Icebreaker Merino 200 Oasis leggings, and while there’s nothing particularly bad about them, we liked some other options better. This lightweight Icebreaker fabric performs well, but it’s not quite as soft as others like the Smartwool Classic. The fit and waistband is not quite as comfortable as our lightweight winner, the Mons Royale Cascade Flex. The Mons Royale is also more than an ounce lighter.

Compare prices of the Icebreaker Merino 200 Oasis Thermal Legging

Icebreaker Merino 200 Oasis Thermal Legging

Arc’teryx Rho Merino Bottoms

Material:  95% Merino wool, 5% elastane
Available sizes: XXS-XXL
Waist: High-rise
Weight: Midweight - 240g/m2
Garment Weight (size L): 7 oz 
What we liked: Same great styling and fit of the synthetic Rho bottoms
What we didn’t like: Sizing way off, very sheer fabric

The Arc’teryx Rho Merino Bottoms seemed like it should’ve been a hit with the same cut and styling of the Rho and Rho Heavyweight bottoms that we love so much. However, the Merino version was disappointing.  

Sizing runs at least a full size smaller than the synthetic version—a size medium was a good fit in both the Rho and Rho Heavyweight for me, and I couldn’t even get the size medium up my legs on the Merino version. I exchanged for a size large and they  fit, though they are still on the tighter side because they lack the stretch of the synthetic versions.  

In addition to the sizing issues, the fabric was sheer and delicate. I would not want to wear these as standalone leggings, which renders the pocket useless. 

Compare prices of the Arc'teryx Rho Merino

Arc'teryx Rho Merino

Why you need long underwear

The benefits of long underwear

Long underwear is essential for outdoor activities to provide insulation and moisture management to keep you warm and comfortable in cold conditions. Long underwear allows for versatility with layering under other garments like hiking pants or hard shell snow pants.  Other baselayers like winter running tights that are designed to be worn alone are bulkier and often have features like pockets that don’t fit well under layers. In contrast, hiking tights don't layer as well as long underwear and are often bulkier with more pockets. 

Icebreaker 260

Using long underwear for layering

Layering allows you to adapt to variable conditions, and long underwear serves as the foundational layer. Long underwear is recommended when the temperatures fall below freezing, or even warmer if you tend to get cold easily.  Outdoor winter activities like skiing and hiking can also expose you to chilly winds and snow. Making sure you are dry and warm is essential, and that starts with an insulating and wicking baselayer right against your skin. You can learn more about layering for cold weather activities in our guides to How to Hike in Winter and How to Layer for Skiing

Versatility for various activities

A good base layer can be worn for all kinds of activities, from hiking and snowshoeing, or skiing, to simply hanging out by the campfire, keeping you warm and dry while still allowing a full range of motion. 


Arcteryx Rho Synthetic

What to look for in long underwear

  • Material

One of the biggest considerations in selecting a base layer is the choice of material.  Synthetics, primarily polyester and nylon, are great at moisture wicking, are quick to dry, and are affordable.  One of the biggest potential downsides to synthetics is their tendency to get smelly.

Cotton is also a common long underwear material (think cartoon long johns in a waffle texture) and while comfortable and cozy for lounging around the house, cotton holds onto moisture, making it a poor choice for active pursuits and outdoor activities.  

Wool as a next to skin baselayer may sound uncomfortable, but merino wool (from merino sheep) is a soft, natural fiber that is comfortable, and offers excellent insulation properties. It regulates body temperature, wicks moisture away from the skin, and even resists odor. Merino wool is ideal for outdoor activities and can be worn for extended periods without getting funky.  While a great material choice, it is generally the most expensive fabric option.

Best Long Underwear for Women
  • Insulation and thickness

Weather conditions, temperatures, and activity type will determine how much insulation you need in your baselayer. Colder ambient temperatures will of course warrant heavier insulation to stay warm. However, your body will produce more heat with high output activities, like snowshoeing or strenuous hiking, and selecting too warm a layer will result in excessive heat and sweat.  

Warmer base layers are generally referred to with terms like “heavyweight.” 

Merino weight is generally specified in terms of grams per square meter of fabric.  Common weights are:

  • Lightweight: ~200 gsm or less

  • Midweight: ~250 gsm

  • Heavyweight: ~300 gsm or more

Smartwool Intraknit
  • Moisture-wicking

Both synthetic and merino wool perform well at wicking moisture away from the body. This is important to keep you dry and comfortable, as well as keep you warm.

The author changing out of base layers in a trailhead parking lot in Washington post-adventure.

The author changing out of base layers in a trailhead parking lot in Washington post-adventure.

  • Breathability

Breathability is key to allow some air circulation, regulate temperature, and prevent moisture buildup, keeping you from feeling clammy. Synthetics can do a good job of this depending on the construction of the fabric, and merino excels at breathability.

Icebreaker Oasis 200
  • Fit

Proper fit is key to a comfortable, well-performing base layer. Bodies come in a wide range of shapes and sizes, and different brands, styles, and construction methods will fit everyone a bit differently. Well-fitting waistbands that stay put and prevent the long underwear from sliding down are key.  A snug next-to-skin fit that isn’t constrictive will provide the best insulation, moisture wicking, and comfort. 

Best Long Underwear for Women
  • Design

Design details can improve fit, function, and comfort.  Look for wide elastic waistbands that distribute pressure evenly and prevent rolling or digging into your skin. Flat seams reduce bulk and irritation and are more comfortable against the skin.  Paneled construction can help the fit better contour to the body.  Gusseted crotches reduce seam bulk and chafing, and allow for better range of motion.  

Ridge Inversion Merino
  • Durability

Durability is a key consideration in selecting a base layer since it is worn for so many activities and will see a lot of use. Fabric and seams need to hold up to extended use and laundering.

Icebreaker 260
  • Sizing

Long underwear is typically sized in straight sizing (XS through XL). Icebreaker and Smartwool offer extended sizing (up to 2X and 4X, respectively) in some styles.

  • Odor resistance

Merino takes the cake in odor resistance and can be worn many times without washing and without smelling bad. Synthetics need to be washed more often to prevent unpleasant odor accumulation. Check out our Best Sport Detergents guide here.

  • Ease of care

Synthetics are the easiest to care for, easily machine washed and dried. Merino wool may sound intimidating, but it’s surprisingly easy to care for. We machine wash all our merino, and even throw it in the dryer on low heat sometimes (manufacturer recommendations vary, but some do endorse machine drying on low heat).  

All garments, regardless of material, will last longer if washed less frequently and line dried.  Thanks to its odor resistance, merino needs to be washed less frequently, so line drying it on occasion isn’t too much of a hassle. 


Best Long Underwear for Women

Buying advice

What activity or activities are you buying the long underwear for?

When considering which long underwear is best for you, consider first the type of activities you’ll be engaging in and the weather conditions you’ll experience. With high output activities like snowshoeing or backcountry skiing, a lightweight layer will likely be a good choice, whereas you may want a warmer layer for hiking in cold weather, or resort skiing where you may spend a significant portion of your time waiting on a ski lift. 

You'll also want to consider the fit of the garment and how it works with your other layers and equipment. For example if you're backpacking ask yourself, "Iis the waistband comfortable under a backpack hip belt?".

You should also consider what type of material you prefer. The natural fibers of merino wool provide outstanding breathability, moisture wicking, and odor resistance, while synthetics dry the most quickly and are typically more durable and less expensive. 

Arcteryx Rho Heavyweight

What specific weather conditions will you be facing during your outdoor activities?

Outside temperatures and types of activities will be the main drivers of how warm a baselayer you choose. The colder it is, the heavier-weight bottoms you’ll want. However, if you’ll be generating a lot of heat with your activity, you will want to go a bit lighter on the baselayer.  

Rain and snow will also factor into your choice.

Do you prefer the natural insulation of merino wool or the quick-drying properties of synthetic fabrics?

If you anticipate wet conditions, you may prefer a synthetic baselayer as it will dry more quickly. However, merino still insulates well even when wet, so if you’re only out for the day, merino can still be a comfortable choice. Extended trips may benefit from synthetics that will dry out more quickly, but merino will stay funk-free longer than synthetics, which tend to build up smells rather quickly. 


Care and maintenance tips

Always allow your long underwear to dry out completely after use to minimize odor buildup.  Washing with cold water and on the gentle cycle will help extend the life of all garments, including long underwear. Line drying is best for long garment life, but a dryer on low heat can also be used.  

Avoid bleach, which is harsh on the fibers, and fabric softeners, which cause residue buildup on the fibers, affecting their moisture wicking and odor preventing properties.


Smartwool Intraknit

FAQ

Can I wear long underwear in warmer weather?

Yes! Long underwear is perfect for warmer weather trips where the mornings/evenings may be cooler. This is especially true at high altitudes. You can wear your base layer until the temperatures warm up and then remove them when it’s comfortable. Base layers can also provide some level of sun protection while still remaining breathable, so pairing with shorts or a skirt for additional coverage can be a good option.

How do I prevent long underwear from becoming too hot or sweaty?

A good base layer fabric, such as merino or a highly breathable and wicking synthetic, will help manage heat. Choosing the right warmth level and appropriate outer layers is also key. Think about how you’ll feel after the first 15 minutes of your activity — you’ll probably warm up considerably as you move, so dress for that condition rather than being fully toasty to start out.  

Can I wear long underwear for multiple days during a trip?

Yes! Allow your long underwear to dry out if it gets wet or sweaty to keep odor down. Merino wool is particularly good at preventing odor buildup and can be worn many days in a row without smelling bad.

Icebreaker Merino 200 Oasis Thermal Legging

Should I wear underwear under long underwear?

This is a personal choice, but most people will likely prefer to wear underwear with their long underwear. The fit of regular underwear may provide a tighter fit and better comfort and protection against chafing than long underwear alone. Additionally, the additional layer of regular underwear will help keep your long underwear fresher and extend the time between washings.  

What is the best long underwear for skiing and snowboarding? 

Long underwear bottoms in a ¾ length cut are ideal skiing, since you don’t want extra bulk inside your ski boots.  Winning models we reviewed that have cropped length options: 

Decide on your preference for merino vs synthetic and how heavy/warm is best for the conditions and locations you'll be skiing.


We wore long underwear until mountaineering and ski pants on adventure trips all winter. Here the author is changing out of wet outer pants in a trailhead parking lot.

We wore long underwear until mountaineering and ski pants on adventure trips all winter. Here the author is changing out of wet outer pants in a trailhead parking lot.

How we researched and tested

We tested these base layers during winter, mostly in the Pacific Northwest. Activities included cold and rainy hikes up to 30 miles in length, and snowshoe adventures and hut trips in the Gifford Pinchot and Mt. Hood National Forests, and even a winter summit of Mt St Helens. 

We also ventured out to the Trans-Catalina Trail in California to ring in the New Year and braved a frigid spring break packrafting trip in Utah. In all, I've been testing women's long underwear for nearly 6 months on everything from cold weather hikes after work to mountaineering ascents. This guide on women's long underwear is based on hundreds of hours of testing in cool and cold weather in Oregon, Washington, California, and Utah.


Kate Hoch Backpacker Outdoor Writer

About the author / Why you should trust us

By trade, I’m a test engineer designing and building machines to test the reliability of forklift components. I’ve put this engineer’s mindset to work when refining my backpacking gear choices over the years, honing in on details, learning about the nuances of material and design choices. 

I’ve been on the board of ALDHA-West (American Long Distance Hiking Association - West) most of the past decade. As part of our annual pre-backpacking season educational events (called “Rucks”), I’ve conducted many pack shakedowns and been a panelist on lightweight gear forums. I’ve shared my knowledge and expertise with hundreds of new backpackers. Running these events also keeps me on top of the newest available options for all kinds of backpacking gear.