The Best Base Layers for Women in 2023

Base layers are essential if you plan on recreating in any season that’s not summer. Whether you’re hitting the slopes, tackling a high alpine peak in cool weather, or just walking the dog on a frigid day, quality base layers can mean the difference between feeling hypothermic or comfortably navigating your day.

Our advice is to get the best base layers for the climate where you recreate the most. Merino wool tends to be a top performer, but yak wool and a few other wool-synthetic blends can also be great in extra-cold environments. Compared to synthetics, wool has the bonus of holding warmth even when wet. It’s also the best for beating back scent for long periods of time like multiday hut trips.

But synthetic fabrics have a lot to offer. They’re often more affordable. And while you tend to give up some odor control, synthetics are the fastest-drying base layers. Fabric options like Patagonia’s well-regarded Capilene are a top choice for aerobic activities where you’ll work up a sweat, thanks to their quick-drying properties. Fibers with the ability to dry fast are especially useful in cold, overcast environments where you can not easily change layers.

Base layers are also made in various densities, and each one provides a different amount of warmth and hand feel. If you want to learn more about base layers, jump down to the buyer’s guide and FAQ at the bottom of this article. Also, have a look at our comparison chart to steer your decision-making.

Otherwise, read on for our top picks for the best base layers for women in 2023:

The Best Base Layers for Women of 2023

Best Overall

Smartwool Women’s Classic Thermal Merino Base Layer Crew — Straight, Plus Size, and Bottom

Smartwool

Specs

• Weight 218 g (top), 208 g (bottom)
• Fabric 100% merino wool
• Thermal category Midweight

Pros

• Super soft
• Comfortable cut
• Crossover use outdoors and for professional meetings or social meetups

Cons

• Does not fare well in washing machine

Morgan Tilton

Smartwool is ubiquitous in the world of base layers, and our team found this set to perform well across a myriad of conditions while also being cozy and comfortable with a clean style. Overall this kit is a top-selling base layer for women.

The Women’s Classic Thermal Merino Base Layer Crew and Bottom (which was originally launched under the name Smartwool Merino 250) keeps you warm for $110 but isn’t overly warm for most activities.

You’ll find 100% merino in this best choice, and that’s just because it works so dang well. Women love both the fit and feel of this easygoing crew and pant, and the fit is right on target. This is also a size-inclusive piece: the top is available for plus-size women in 2X and 3X.

According to customer feedback, the plus sizes are on the money for some, while others would like to see a 4X option added to the lineup and a few inches in length for the option of layering a shirt beneath. And the bottom is available up to 3X.

After months of winter wear, we can attest this base layer kit is a top performer. We especially love the softness and next-to-skin comfort as well as the ease of layering. The durable construction feels denser than a handful of our other favorite base layers, like the Le Bent Le Base 200 Lightweight Crew.

We’ve worn dozens of midweight layers. The Classic Thermal Merino Base Layer set performs beautifully across temp ranges and is one of our go-to choices for winter activities like skiing and snowboarding at the resort with stagnant breaks in the ski lift line or while riding up. Overall, the merino does a great job of masking stench, too.

For some of our uphill, backcountry, and nordic ski testers, this kit feels a bit warm and heavy for high-cardio activities.

Check Straight-Size Price at REICheck Plus-Size Price at REICheck BottomS Price at REI

Best Budget

Helly Hansen HH Lifa Crew Performance Base Layer

Helly Hansen

Specs

• Weight 108 g
• Fabric 100% polypropylene (Lifa)
• Thermal category Lightweight

Pros

• Nice option for high-output activities
• No itchiness
• Great wool-free choice

Cons

• No thumbholes
• Not very insulated

Morgan Tilton

One of the longest-standing base shirts we pull on for high-cardio snow sports is the Helly Hansen Crew Performance long-sleeve top. And at only $45, that price tag is hard to beat for the decade-reaching quality without a single unraveled seam.

This extremely lightweight and breathable design doesn’t make us feel claustrophobic on a bell-to-bell powder mission or ringing mogul after mogul. The pull-on smoothly wicks sweat and doesn’t hold onto the moisture. The seams never rub or annoy our skin, even on the more sensitive folks.

You’ll be giving up insulation for this base layer, which really shines for breathability. That also means this base layer is super versatile, because it can be pulled on for sledding, cross-country, or alpine skiing and backcountry tours without becoming an oven. You can always wear a thicker mid-layer if more warmth is needed on those frigid days or sedentary activities.

The fit on the Crew Performance long-sleeve top is not too snug, either, but if you prefer an even looser fit, check out the men’s cut instead.

Check Price at AmazonCheck Price at Helly Hansen

Best Plus-Size Budget Set

REI Co-op Lightweight Base Layer & Top

REI

Specs

• Weight 218 g (top), 208 g (bottom)
• Fabric 92% polyester, 8% spandex}
• Thermal category Lightweight

Pros

• Comfortable against skin
• Hems are not too tight
• Wicks sweat well

Cons

• Some found the pant material around the calves and thighs to be loose

Morgan Tilton

We were pleasantly surprised to see REI has plenty of offerings for base layers for plus-size women, between Smartwool and the REI Co-op brand. And the affordability and positive reviews on these bottoms ($40) make them a shoo-in for gals who’ve often felt left out of the world of athletic clothing.

And women of all sizes really do love this shirt ($40). The size range for both include 1X, 2X, and 3X. Some ladies found that the top is snug around bust area for larger-chested ladies so, if that could be you, consider sizing up.

This is a lighter base layer but will get you through a ton with a fitted poly-spandex mix. If you want to level up and go merino, check out Smartwool’s $110 250-weight legging and top.

Check Bottoms Price at REICheck Top Price at REI

Warmest Base Layers

Kari Traa Rose Half-Zip & Rose Wool High Waist Pant

Kari Traa

Specs

• Weight Unavailable
• Fabric 100% merino wool
• Thermal category Midweight

Pros

• Extremely warm
• Quality construction
• Long arms cover wrists

Cons

• Merino wool blends wear down quicker than synthetic

Morgan Tilton

Merino continues to dominate, and the Kari Traa Rose Half-Zip ($120) brings a classic ski lodge feel to the list. Offered only in fashionable Nordic patterns, this 100% merino half-zip and the Rose Wool High Waist Pant ($110) have a feminine touch with an athletic makeup.

Developed by an Olympic skier, Kari Traa’s base layers also have amazing design features like underarm gussets, a more athletic fit around the shoulders and hips, and a hugging four-way stretch construction.

Our editors have been impressed after testing out the Rose Half-Zip. It performs well doing laps on the slope, and the zipper never jabs or digs into your skin (just make sure you get the right size). During spring skiing, you can shed your hardshell and retain warmth with this layer.

Speaking of warmth, the Smartwool Women’s Classic Thermal Merino Base Layer Crew and Bottom are likewise midweight, 100% merino wool designs — so which kit is warmer? Technically, the Smartwool setup is a fabric weight of 250 gsm.

The Kari Traa is 240 gsm with underarm side panels that are 180 gsm, which help dump heat while working up a sweat on a powder day. We found the extended collar on the Kari Traa top provides a bit more coverage and warmth.

Ultimately, similar to the Smartwool set, this Kari Traa design has a high warmth-to-weight ratio. Some of our testers prefer to wear this Kari Traa base layer set at the ski area when the temperatures hover below 20 degrees F plus windchill. The Kari Traa kit also pairs well for backcountry skiing in the 0- to 10-degree F range and definitely for temps in the negatives. The fabric weight can feel a bit too warm for high-output activities in warmer temps.

While this set provides top-tier warmth, the blend can feel a smidge itchy for some with really sensitive skin. The textile also lacks a bit of stretch that other blends provide. All things considered, this Kari Traa top and Bottom are still our go-to pair when warmth is the number one priority.

If you do reach for this lovely design, the look is great, too. Read our full review. For a slightly looser fit and similar style, check out the Kari Traa Else Wool Pant ($100) and Else Wool Half-Zip ($110).

Check Top Price at REICheck Bottoms Price at Kari Traa

Best Set for Workouts

Ortovox 185 Rock’N’Wool Long Sleeve & Short Pants

Ortovox

Specs

• Weight 142 g (bottom), 164 g (top)
• Fabric 100% merino wool
• Thermal category Lightweight

Pros

• Feels lightweight
• Durable
• Comfortable for layering and dynamic movement

Cons

• Pricier investment

Morgan Tilton

Ever since we pulled on the Ortovox 185 Rock’N’Wool Short Pants ($100) and Long Sleeve ($110) set for winter action, this comfortable, breathable kit has been one of our go-to sets for backcountry skiing, snowmobiling, shoveling, and resort powder days. Any time we are going to be working hard and breaking a sweat, this is our first choice.

When we wear this pair, we can’t feel it at all. The airy blend pulls up moisture and dries fast, and the seams don’t feel restrictive.

We like that the pant legs reach below the knee, so we don’t need to layer them over our socks. The waistband sits comfortably above the hips. And the fabric does a great job of covering up body odor after a long haul or uphill workout.

The kit is also climate-neutral and Fair Wear certified. This design complies with the ORTOVOX Wool Promise, which is a higher benchmark than the Responsible Wool Standard, according to the brand. While merino wool is the top-tier for baselayer construction, you’ll also pay for it — this set is pricey, but we believe 100% worth it.

We’re wearing the 185 Rock’N’Wool Short Pants and Long Sleeve more often than it’s hanging in our closet when winter comes. Perfect for athletic days in the hills, this set excels in motion.

Check Top Price at BackcountryCheck Bottom Price at REI

Softest Base Layer

Le Bent Women’s 200 Crew

Le Bent

Specs

• Weight 200 g
• Fabric 66.5% rayon from bamboo, 28.5% merino wool, 5% elastane
• Thermal category Lightweight

Pros

• Extremely soft
• Versatile contoured fit for the ski slopes, town, or meetings
• UV 50+ protection

Cons

• Not a heavyweight choice for stagnant winter moments like glassing for elk

Morgan Tilton

This could be the lightest, softest, stretchiest, most attractive base layer top we’ve ever worn. We want to use it for everything outside and inside, even going out to dinner. We wore the Le Bent Women’s 200 Crew ($95) nonstop for several days of outdoor activity in the Colorado Rockies including frigid, windy trail runs, wintry walks, and even sleeping.

The shirt’s buttery blend features bamboo rayon, merino wool, elastane, and four-way stretch. The arms and torso are long, so no skin is exposed in extreme temperatures or wind chill. And the fabric masked odor for multiple days despite sweaty back-to-back action. This is the perfect do-it-all layering piece during and post-sport.

Our only issue is that there aren’t more heavyweight options — we would love a thicker weave for more static endeavors — but barring that, the Le Base 200 Crew covers our need for luxuriously soft base layer tops for winter. The fabric has only starting to show slight pilling after several seasons, so it’s robust, too.

Check Price at Amazon

Most Sustainable

Daehlie Compete-Tech Pants

Daehlie

Specs

• Weight Unavailable
• Fabric 50% recycled polyester, 30% Tencel Lyocell, 20% merino wool
• Thermal category Lightweight

Pros

• Lighter option for warmer or action-packed days
• Smooth and easy to pull on
• Sustainable design

Cons

• Not super warm for really cold conditions while sitting on the ski lift

Morgan Tilton

For a lighter-weight, performance-oriented bottom that cares about where it comes from, check out the Daehlie Compete-Tech Pant ($60). After using these pants for alpine skiing and backcountry skiing as well as skimo workouts, we can confidently say it covers up smells and never snags during movement.

We also appreciate the steps that Daehlie takes for sustainability. The merino wool used in the blend is non-mulesing, traceable, and certified by the International Wool Textile Organization. The polyester is 100% recycled.

The main fabric contains 30% Tencel Lyocell fiber, which is made from the pulp of a fast-growing eucalyptus tree, which the brand sources from a farm certified by the Forest Stewardship Council. There’s no genetic modification. Also, the chemicals used to produce the fiber are recycled, reducing hazardous waste.

Strategically placed panels around the knees dump heat and wick sweat, and all of the fabric dries fast. Overall, this base layer does a nice job of managing a range of temperatures while moving big. It’s also a streamlined base layer to pull on beneath pants for errands around town during cold spells or on windy days.

While not the baselayers we’d grab for the coldest days of lift-access skiing (these are a bit too lightweight), the Compete-Tech Pant from Daehlie is perfect for those who still desire high-functionality when it comes to their sustainable clothing.

Check Price at Daehlie

Best of the Rest

Kora Yushu LS Crew

Specs

• Weight 230 g
• Fabric 100% yak wool
• Thermal category Midweight

Pros

• High-rub areas feature reinforced thread for durability
• High-quality construction
• We appreciate the lengthy arms

Cons

• A bit pricier
• Not as versatile across all temperatures

Morgan Tilton

Kora base layers are made out of yak wool, and this stuff performs. It’s pricey at $130, but only a bit more pricey than merino, and it tends to be warmer for less weight.

In our experience, that’s a bit of a toss-up unless the weather is really cold. We tend to use our Kora layers as heavyweights rather than midweights, as they’re just a bit too warm for early to mid-fall for what we’re up to.

This crew is a constant in our winter kit. It’s thin enough to easily go under sweaters or fleeces for added warmth, and it’s nice enough to wear on its own with a vest on warmer days. Yak wool really does pack a warm punch. If you’re doing legit stuff in cold weather, invest in the Kora Yusha LS Crew.

Check Price at Kora

Voormi Women’s Base Layer Bottoms & Long Sleeve Baselayer Crew

Voormi

Specs

• Weight 195 g (pants), 208 g (top)
• Fabric Proprietary wool and synthetic fiber blend
• Thermal category Midweight

Pros

• Super durable
• Shields water and sweat extremely well
• Athletic fit prevents chafe

Cons

• An investment
• Seams are not as stretchy as less durable options

Morgan Tilton

Voormi’s thermal base layer bottom ($119) is one of our top choices for backcountry skiing and splitboarding, resort skiing and riding, post-adventure après, and year-round camping. One of our favorite details about this unique and tenacious fabric blend is that beads of water roll right off the surface, so these bottoms don’t get soaked.

The brand’s Women’s Long Sleeve Baselayer Crew ($119) is constructed with the same material: Dual Surface precision-blended wool technology, which boasts a thin interior layer of fine micron-wool that pulls moisture off the body and disperses it to the exterior, blended with a portion of polyester and nylon. The fabric is soft against skin yet has an extremely durable exterior.

Despite back-to-back usage, the pants and shirt don’t reveal odor. We’ve taken multiple hut trips packing only these base layers in a range of climates and conditions from gripping-cold blizzards to sunshine. Our sweat and any water patches dry fast, and the wool works it magic with regulating temps, so we never feel damp or clammy in these long johns or top.

This blend is lightweight for the density and warmth provided. The material and seams hold up through arduous usage beneath snow pants and work pants in all seasons. They aren’t quite as stretchy as other baselayer options we tested, but we appreciated the inverse effect of not sagging. As a result, we don’t particularly like using the top’s thumbholes, which feel a bit too restrictive.

If you’re looking for a bottom that hugs your legs and doesn’t slouch a bit on high-action days, the Voormi thermal base layers are worth the investment. The same goes for the Voormi long sleeve baselayer crew.

Check Bottom Price at AmazonCheck Crew Price at Amazon

Black Diamond Solution 150 Merino Baselayer Crew

Black Diamond

Specs

• Weight 146 g
• Fabric Nuyarn 78% merino wool, 22% nylon
• Thermal category Lightweight

Pros

• Fine, stretchy 18.5-micron merino wool
• Thumbholes

Cons

• We wish the length was more generous

Morgan Tilton

Black Diamond uses a wonderful merino wool blend called Nuyarn in its Solution 150 Merino Baselayer Crew ($135), and multiple members of our testing crew love the material.

Nuyarn gives users the best of both worlds, with the odor resistance and soft hand of merino combined with the durability and quick-drying nature of nylon. The blend is breathable and the fit streamlined — we love that there’s no bulk.

It’s a simple design of this fabulous fabric, featuring just thumb holes to keep the layer in place on the arms when pulling over second layers. The torso length was a smidge short for some of our testers — one of our only issues — but layered under another piece it becomes less of an issue.
Overcoming the traditional pitfalls of merino wool, we loved the stretch and durability of the Solution 150 Merino Baselayer Crew.

Check Price at Black Diamond

Arc’teryx Motus Crew Neck LS

Arc'teryx

Specs

• Weight 125 g
• Fabric 100% polyester
• Thermal category Lightweight

Pros

• Soft against skin
• Moderate price
• Fairtrade certified

Cons

• Not extremely durable for alpine and rock climbing according to some users

Morgan Tilton

Once the temps drop, we grab this just-right base layer for trail runs or uphilling at the ski area. The Arc’teryx Motus Crew Neck LS ($80) pulls our sweat and dries like a champ, so no wonder it remains a top-rated item.

The exterior fabric is treated with a DWR finish to barricade dew and drizzles, so we can skip a mid-layer if it’s warm enough out and not pounding snow. We like the mini turtleneck style, which offers a boost of protection for our décolletage and blocks drafts.

The shirt is designed for ultimate freedom of movement, so side-to-side motion or planting poles don’t feel held back. And the seams don’t feel bulky, either.

Check Price at Arc'teryx

CEP Ski Touring Base Shirt & 3/4 Base Tight

CEP

Specs

• Weight Unavailable
• Fabric 44% polyester, 29% Lyocell, 8% polyamide, 8% wool, 6% spandex, 5% cashmere
• Thermal category Lightweight

Pros

• Sweat dries fast
• Fairly soft

Cons

• Only one arm has a thumb hole
• For some folks the mock turtleneck can feel a bit restrictive

Morgan Tilton

This performance-oriented design is form-fitting, so if you don’t like apparel that hugs, skip ahead. In a unique approach, CEP recently launched compression-style base layers.

After giving this top ($100) and bottom ($100) test runs at the ski area and in the backcountry, and while sitting sedentary, the compressed feel is noticeable at total rest post-activity. The set is also comfortable to wear while on the go.

The pants reach below the knee, which we like for streamlined layering with our socks and boots. The anatomically designed threads support the hamstrings and quads, and the high-tech fabric manages sweat and heat.

For some folks, the compression fit can be a bit much, notably in the neck. It’s a good idea to experiment with compression clothing before pulling the trigger on these winter-weight baselayers.

Rounding out the CEP Ski Touring Base Shirt and 3/4 Base Tight are super smooth chafe-free seams in the top and bottom that are anything but noticeable. We also like that these base layers dry fast.

Check Top Price at AmazonCheck Bottom Price at Amazon

First Lite Kiln Hoody & First Lite Kiln Long Jane

First Lite

Specs

• Weight 425 g (top), 227 g (bottom)
• Fabric 95% merino wool, 5% spandex
• Thermal category Midweight

Pros

• Excellent quality
• Ideal versatile weight

Cons

• Top can feel tight around broader shoulders and some opt to size up
• Size large pants can be a bit loose around the waist

Morgan Tilton

Can we live in our First Lite Kiln Long Janes ($95) and First Lite Kiln Hoody ($130)? The answer is yes, and we have. We’ve worn these feminine long janes for days on hunts, only to find that they stave off body odor better than any other we’ve tried, even after hours of hiking and packing.

And hoodies are either your jam or not. We like to wear this one when we know we want a second layer to keep our head warm beneath a hat or when the weather isn’t bad enough to require a shell hood.

These things just beat back odor, wick and breathe like magic, and fit in a way that eliminates bulk. If you caught us wearing either, you’d likely think it was a new purchase. Fewer washes beget longer use times. We’re into it.

Another benefit to remember with paying more for wool is if you get wet, you still retain heat. Synthetics might dry faster, but the warmth merino offers is a big plus. The design is also made with 18.5-micron fibers, which is superfine merino wool.

High-waisted, soft, and with seams in the right spot to avoid backpack misery, these leggings are made for women and are our favorite fit of any base layer we’ve owned. That said, the size large pants tend to slide down for some users, so beware.

Merino rules the day, and these are opaque enough to wear as a first layer on warmer days with no issues. With a 250-gram merino and spandex woven fabric, these are a true midweight pant.

But in our humble opinion, they’ll get you through the great majority of cold situations with no problem. We’ve worn ours for a few years, and they feel practically new.

Though First Lite is a hunting brand, it offers its Kiln Long Janes and Kiln Hoody in solids for those of you who might not need camouflage in your life.

Check Top Price at AmazonCheck Bottom Price at Amazon

Base Layers for Women Comparison Table

Why You Should Trust Us

Our GearJunkie product testing team includes a range of skiers and snowboarders from intermediate to expert who explore ski areas around the world, venture into the backcountry, skin uphill at the resort, and enjoy nordic trails.

Our team also includes avid hunters and folks who live in wintry, cold, mountainous locations from Bozeman, Montana, to Crested Butte, Colorado. We backpack, hunt, and track elk in the shoulder season.

Throughout our field tests and personal experience, we determine the best women’s base layers based on a variety of metrics including performance, quality, comfort, fit, longevity, and value. We take a close look at each product’s warmth, breathability, wicking and drying capability, weight, density, seams, hems, cut, next-to-hand feel, and style.

We also consider the most innovative, sustainable, legacy, award-winning, and popular designs on the shelf today. Hands down, these base layers serve a wide range of athletes, applications, and budgets.

Buyer’s Guide: How to Choose the Best Base Layers

Start by imagining how you’ll use these base layers. Are you looking for something extra warm for relaxing around camp? Or will you be working hard in the backcountry and need a breathable, fast-wicking layer?

There’s no right or wrong answer, but knowing how you’ll use these layers will help narrow the field.

Styles of Base Layers

Technically, base layers feature a range of designs including tank, long-sleeve, and short-sleeve tops, as well as ankle-length or capri pants. In our guide, we focus on the best options for cold weather and the winter season, which are usually long-sleeve tops and ankle-length bottoms.

The fabric blends of base layers include merino wool, synthetic fibers, or a blend of the two. Within those fibers, there are various densities from lightweight to midweight or heavyweight. Some tops feature a hood, partial zipper, or thumb holes. Others are tailored with a crew, mock, or turtleneck.

Base layers are absent of pockets or belt loops. These designs are meant to be worn against the skin in a seamless way that’s comfortable beneath other mid-layers and outer layers across various activities such as hunting. fishing, hiking, skiing and snowboarding, snowmobiling, or working on a farm.

Fabric Blend

Merino Wool

We love wool. It regulates temperature really well. It’s fast-drying, comfortable against the skin, and resists odors like a champ. It’s the warmest fabric choice for low-intensity outdoor activities like ice fishing or spectating ice skating.

That said, 100% merino wool tends to be less durable, gets wear holes more quickly, and gets baggy throughout the day. If you have sensitive skin, even the smoothest 100% merino wool might feel a tad less than cloud-like next to the skin. Depending on your preference, you may prefer a wool blend or straight synthetic materials.

Merino wool can also cost more than its counterparts.

Synthetic

An alternative to wool is a synthetic fabric, which is typically a blend that includes polyester plus elastane or spandex for rebound and form. Some synthetic fabrics are proprietary to a brand with treatments that enhance their odor-fighting ability and wicking moisture.

Synthetic blends do not offer as much warmth and overall temperature regulation that wool provides. They’re a great choice for high-intensity activities that produce a lot of perspiration without long moments of standstill, like during a hunt, when a chill could set in.

These fibers can work really well for people with sensitive skin, especially for exercise use. The breathability is still excellent and really only a hair less impressive than merino wool or wool-synthetic blends. Also, synthetics typically cost less than wool.

One drawback: Odor-intense days are not typically covered up well by this fiber.

Wool-Synthetic Blend

Many folks find a fair balance of managing heat and chill, absorbing sweat, and covering up odors in a design that weaves together both wool and synthetic fibers. Adding synthetics also enhances the durability and overall life of wool apparel.

Insulation Weight 

Lightweight

If you’re running hardpack snow trails, snowshoeing, skate skiing, or doing uphill ski workouts in 30-degree temps, a lightweight base layer top or bottom should do the trick, as long as there’s no wind chill.

Lightweight layers dump heat really well. These could be a good piece for warmer spring laps at the ski resort, but sitting idle on lift rides typically calls for a warmer midweight base layer.

Midweight

Not too airy and not too stuffy, the midweight base layer is optimal for wintry days skiing and riding at the resort. It’s a good choice for snowmobiling, when pulling the throttle can pack windchill at high speeds.

That said, for intense heat-building activities like huge ski or splitboard tours or snowshoeing, a midweight layer might be too much.

Heavyweight

When we’re talking extreme temperatures — well below zero or even below freezing — then you might be coziest in a heavy-set base layer, especially for ski resort laps. These are also the layers we grab for sedentary periods.

Those activities include ice fishing, sailing, hunting, spectating events, hanging at base camp during a mountaineering expedition, or even snowmobiling groomed trails, especially if sightseeing stops are frequent.

Fabric Weight

You might have noticed the acronym gsm (grams per square meter) but likely don’t know what it means — which isn’t a surprise. There isn’t a ton of marketing or public education about the label, which is a standard unit for measuring fabric density.

The higher the gsm, the denser the fabric and the warmer it will be. A fluid-feeling blouse might be as low as 50-100 gsm, while denim reaches into the 340-450 gsm range.

Regarding base layers, an ultralight design would be below 150 gsm. Lightweight base layers typically range from 150-195 gsm. A midweight base layer usually falls within the 195-250 gsm range. Heavyweight base layers are above 250 gsm and below 320 gsm.

You’ll want to match your physical exertion to the gsm or your body’s typical needs. If you plan to do high cardio activity, choose a lower gsm.

If you plan to be more sedentary, such as ice fishing, watching a hockey game, or running errands, choose a higher gsm. A higher gsm is also a good option for folks who have poor circulation or tend to get chilled during winter activities.

For easier reading, we didn’t include gsm labels in our selected products in this guide in lieu of sharing the general thermal categories: lightweight, midweight, and heavyweight.

There are base layers that do not weigh very much but have a dense fabric, or gsm, and therefore, a high warmth-to-weight ratio, such as the Kari Traa Rose Wool High Waist Pant, which is categorized as a midweight choice thanks to their density and subsequent warmth.

Qualities

Insulation & Warmth

This ties into end-use. For extra-cold weather or more sedentary activities like ice fishing, sitting in the hunting blind, or relaxing around camp, you’ll want something warmer and with more insulation power. The strongest options will be in that heavyweight label.

If you’re using your base layer for major cardio output, opt for a lightweight design.

Breathability

In addition to trapping heat, it’s important the layer breathes well and efficiently wicks moisture. Freezing sweat will make you colder faster than a too-thin layer. Generally, the lighter a design is, the more breathable it will be. Merino wool is also more breathable than synthetics.

The Smartwool Classic Thermal Merino Crew Base Layer is a warm winter layer that breathes incredibly well. It’s our top pick for the dead of winter but also for alpine pursuits in fall and winter.

If you know you’re going to be busting it uphill on a bluebird day, then look for a lighter layer. Something like the REI Co-op Lightweight Base Layer Long-Sleeve Crew Top will be a key part of your layering system.

Odor Prevention

If you’re packing minimally for multiday use, like a hut-to-hut or mountaineering trip, merino wool does wonders with hiding odors. Generally, synthetic materials don’t champion covering up stench as well as this natural fiber.

Comfort & Fit

There’s nothing more annoying than ill-fitting base layers. From backside or frontside sagging to pulling to chafing, it’s important to find comfortable-fitting long underwear. Things to consider are softness against skin and tightness. You want a base layer to fit snugly against your body while allowing full range of movement.

It’s also important to look at length and seams. You don’t want to gap at the waist. Nor is it ideal to have too-short sleeves or pants.

Seams can cause chafing, so beware of your movement and potential trouble spots. If chafing is a constant problem, you may want to consider the seamless Patagonia Capilene base layers.

Durability

Thermal layers are an investment, so it makes sense you want them to last. Synthetic layers are often more durable but can cause more trouble with retaining odors.

Merino wool is naturally odor-fighting but tends to be more fragile. You’ll want to take care putting them on and use them mostly as true base layers underneath protective pants or other layers.

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