Long underwear, AKA the base layer, has come a long way since the dimpled cotton long johns of our youth. This apparel is designed to wick away moisture from your skin to the outside environment, regulating the temperature between skin and shirt. It is the basis of a layered clothing system, but selecting the right one from the heap of options isn't obvious. Fabric materials and weight play a significant role in each top's performance, impacting critical areas like comfort, breathability, and durability. Worn as a second skin, the fit is also a major factor. Our experts tested and reviewed 12 models in all kinds of conditions and environments from the Andes to the Sierras. The result is a comprehensive review that ranks each product for their best uses so you can quickly find the perfect long underwear solution for your layering needs.
SmartWool nailed it with the Merino 250 Base Layer. For starters, the material is incredibly soft. If you avoid wool because you find it uncomfortable, this might be the model to change your mind. It insulates well for cold-weather activities like skiing, ice climbing, and winter camping, yet regulates temps well enough to be worn on cool hikes. It has a UPF rating of 50+ and doesn't build up a big stench factor. This shirt breathes sufficiently, especially considering its thickness, and it layers over and under other tops and jackets. Lastly, the fit is something to get excited about. With a long drop tail in the back, it covers your bum and stays tucked in. The bottom hem doesn't ride up, and the sleeves stay in place. The weave is elastic, moving with you through all kinds of activity, and the flat seams prevent chafing.
Warm and breathable
Too warm for some environments
On the flip side, this model doesn't dry as fast as several thinner tops we tested. That is offset, however, by the fact that it continues to insulate when wet. It also lacks the durability of comparable synthetic models. The $100 price tag is steep, but not out of the ordinary for wool long underwear tops. There are other products we recommend for specific uses, but for low to moderate activity in cool to frigid temps, this is our go-to first layer. It even looks good après ski!
Read review: SmartWool Merino 250 Base Layer
For fall and spring ventures into the outdoor playground, the Rab Merino+ 160 is an excellent choice. A blend of merino and polyester, the material feels nice against the skin. The fit is slim, mobile (assisted by large underarm gussets), and even flattering. Its ability to breathe and wick away moisture is near the top of its class, moving moisture away from our warm torsos efficiently. If you get wet in this top, rest assured that it dries out quickly. And with its fabric consisting mostly of merino wool, it retains heat better than synthetics when wet. As a first layer, it fits comfortably underneath a synthetic jacket or fleece.
Awesome breathability and drying speed
Slim and mobile fit
Not warm enough for most winter pursuits
This thin top won't last forever, though. The seams are prone to ripping and shedding strings, which we experienced during testing. It's also pricey, ringing in at $110. For winter excursions, this Rab top likely isn't warm enough, especially for low to moderate levels of activity. For shoulder season rambling, we love this top.
Read review: Rab Merino+ 160
Not psyched to spend a hundred bucks on a long underwear top? Welcome The North Face Warm. Simply put, it performs above average across the board and costs much less than other top models. Beyond its price, it's extremely comfortable against the skin. If you are allergic to or can't stand the feeling of wool, this synthetic top has an itch factor of zero. The durability is also top notch. It might get a few snags, but the bomber seams haven't shown much wear at all after a year of moderate use. It will last many use-and-wash cycles.
Fantastic next-to-skin feeling
Price to performance ratio
Requires frequent washes
As with all synthetic models we tested, it doesn't control odor as well as its wool counterparts, so you'll need to wash it more frequently (or struggle a bit more to find a climbing/hiking/tent partner). The fit could also use some fine-tuning. The neck collar is a bit loose, and the sleeves slid down our wrists when reaching overhead, although not as bad as some. These drawbacks are not deal-breakers for the majority of cool to cold weather activity, though. Especially considering that it's a 1/4 zip top (which cost more than crew tops), this model provides a lot of value.
Read review: The North Face Warm
For high-level activity in the cold, the Helly Hansen Lifa Stripe Crew combines performance and value better than the rest. As you heat up in the cold outdoors, a shirt that moves moisture and sweat away from your skin works best, and that's what this top does. With exceptional wicking ability from the thin, lightweight fabric, our testers especially love backcountry and cross-country skiing with this top. Resort skiers dig it as well, as it keeps sweat away when double-poling through the flats while layering under an insulating mid-layer. The Lifa Stripe also dried out faster than any other top on this list. We also liked this top when climbing, mountain biking, and trail running in the cold. Oh, and it's the least expensive top at $40.
Low price and weight
Breathable with fastest drying speed
Sleeves stay in place
Bottom tends to rise up
This is not a quiver-of-one type of base layer. If your activity level is low, it's not going to insulate well, and you'll be cold. One or two uses is all you get before you need to wash out the odor, unlike most wool tops. Plus, Helly Hansen recommends avoiding the dryer (although this shirt dries fast outside the dryer). If you charge hard in cold weather, though, this is an incredible and affordable tool to have in your wardrobe.
Read review: Helly Hansen Lifa Stripe Crew
The Arc'teryx Rho AR is great for those who spend long periods of time in the cold during limited levels of activity. Think long winter belays, ice fishing, and sports spectating. Its thick fabric is super soft and mega stretchy, so it looks and moves great. The snug fit traps heat against the body, and our bare skin was never exposed. This top works as both a first layer or a mid-layer, increasing its versatility. Unlike most long underwear tops on the market, the Rho AR has a small chest pocket for storing small items like keys, ID, or headphones.
Very warm and soft fabric
Wish for more breathability
This top doesn't breathe efficiently, though, making it a poor choice for being active in the cold. Being so warm, it's easy to break into a sweat underneath, despite having a long front zipper to expel excess heat. When wet, it takes a long time to dry too and loses most of its insulating ability. It's also expensive and pills up easily. For hanging out in the cold, though, this model provides ideal warmth.
Read review: Arc'teryx Rho AR
Our favorite base layer for running is the Patagonia Capilene Midweight. It's our lead tester's top choice for trail runs from October to April. The lightweight, synthetic fabric breathes well and dries quickly. The loose fit allows for ventilation when moving, and we like using the thumb loops to increase coverage to our hands in the cold. We didn't experience any chafing on runs up to ten miles, either. A go-to top for running, the Capilene Midweight is also well-suited for cool hikes and similar activity where a thin and durable long-sleeve layer suffices. It's also priced within a dollar of our favorite value-driven model, The North Face Warm.
Lightweight and fast drying
Sleeves and torso rise up
This is a top for mild spring and fall days, not intended to provide a lot of insulation through the winter. When climbing or riding a bike, we wished the cut was longer in the waist and sleeves, as they both rose up constantly. If you have a tight mid-layer you like, this model might not pair nicely; we experienced bunching of fabric in the armpits under snug second layers. That said, this model is light, breathable, and ready to hit the trails with speed.
Read review: Patagonia Capilene Midweight
Nothing stands out about the REI Merino Midweight, but maybe that's the point of a good base layer top. It gets the job done without making a scene. The stitching and fabric are quality, showing minimal signs of wear after the testing period and beyond as we continue to use this top. We like the long drop tail for tucking it into our pants, and the extra length of the 12-inch expels excess body heat when working hard. The fit is neither tight nor baggy, which allows for solid temperature regulation. It's on the lighter end of midweight long underwear tops, and it breathes very well.
Solid performance overall
Extra long zipper for venting
Doesn't wow in any category
There aren't major drawbacks here, but we found a few minor quips. You'll need to look elsewhere if thumb loops are essential to you, and the fit of the zipper isn't the best. It bulges out when zipped up, which negatively affects its profile under another layer and doesn't help this top's appearance. This REI shirt isn't as soft or warm as other contenders either. It is a great base layer, and its shortcomings are only noticed when compared side-by-side to other top-notch products. Feel free to use and abuse this shirt all winter long.
Read review: REI Merino Midweight
The Oasis Icebreaker feels great next-to-skin, similar to the oh-so-soft SmartWool model. The fit is tighter than most across the chest without restricting mobility in the arms, assisted by asymmetrical gussets under the arms. Icebreaker achieved moderate insulation while keeping the weight low. Like all merino wool products, it breathes well, too. It resisted absorbing water and dried out faster than the other wool tops.
Allows wrists and belly exposure easily
Not great worn on its own
Our biggest complaint is the fit. Raise your arms, and wrists and bare midriff up to the belly button get exposed to the elements. This lets out a lot of heat trapped between the torso and inside of the shirt and isn't what you want in chilly weather. We also wish we could throw this top in the dryer when squeezed for time, but that's not recommended to avoid shrinkage. This is a nice top when worn under a mid-layer or shell, but not our favorite on its own due to the fit.
Read review: Icebreaker Oasis
The tasc Base Layer blends bamboo, merino wool, and lycra to form an incredibly stretchy shirt. The flexibility and slim fit make this top feel like an additional layer of skin that was paralleled by no other model. It looks tight without feeling tight, keeps wind gusts out, and stays in place during all kinds of body movement. It's warm, too, aided by an extra-long torso, longer-than-most sleeves, and our favorite thumb loops in the pack.
Moves seamlessly with body movements
Favorite thumb holes
Less comfortable fabric feel than most
The least appealing aspect of this top lies in its weak durability. Following three months of moderate use, we had more loose threads, holes, and tears in this top than any other. The tasc model wasn't in tatters, but we expect longer life from a $90 shirt. It was also on the itchier end of the spectrum, not as soft and cozy as the SmartWool or Icebreaker models. Compared to the other blended fabric base layer from Rab, this model took much more time to dry out, too. If mobility is your number one need, this shirt is worth it despite its drawbacks.
Read review: tasc Base Layer
The Minus33 Isolation Midweight Wool offers the lowest price for a 100% merino wool top among all contenders. The fabric is thick and durable. It's pretty warm and works fine as a first layer for a low-output activity like fishing or hunting from a deer stand in the cold. It's even offered in camo, indicating its consumer target.
Low price for merino wool
50+ UPF protection
This top fell short of our favorites list for a few reasons. The baggy fit meant that it wasn't as warm as expected for its thickness, and also detracted from its breathability. Its thick seams were more noticeable than on other tops, and it isn't flattering. It's not a high-performance top, but more substantial torsos will benefit from the loose fit. And for the price, it's still a decent option.
Read review: Minus33 Isolation Midweight Wool
If you need a base layer top to slip on underneath your jersey or team uniform, put the Under Armour Base 4.0 on your shortlist. It doesn't provide a ton of warmth, but that's not the intention. It's ideal for mid to high-intensity sports where your body produces the majority of the heat you need. The Base 4.0 keeps the chill away with excellent breathability, allowing a rapid transfer of sweat and moisture from the inside to the outside of the shirt. The tight fit allows for a jersey to easily slide over top.
Waffled cell construction increases breathability
This top isn't well-suited to a wide variety of applications, though. The tight fit was constricting when moving our arms, the neck squeezed too tight on some testers, and the thumb loops dug uncomfortably into our hands. It wasn't uncommon to need to adjust the sleeves or hemmed waist of this shirt. We also expect the tight fit to put extra stress on the seams, leading to durability issues down the road. It isn't suited for the backcountry, yet for workouts in cold weather to snowy soccer games, this base layer is a fine choice.
Read review: Under Armour Base 4.0
The Mountain Hardwear Microchill 2.0. Is it a first layer? A mid-layer? Perhaps both. Mountain Hardwear brings their reputation for high-quality materials and construction to this top, which has bomber seams and a thick material that resisted all the abuse we put it through. It's also one of the warmest tops, due largely to its thick, soft fabric. The Microchill also comes in at a low price, which we can all appreciate.
Preferred as a mid-layer
Compared to other base layers, though, this microfleece layer fell behind. It's heavy, dries slowly, and doesn't breathe well. The soft texture of the fleece was offset by the large, embroidered logo that felt very itchy against our chests. The thick seams over the shoulder aren't our favorite, either, when worn under a pack. It isn't a great choice as a first layer. After trying it both ways, our testers preferred to wear this top as a mid-layer. If you want a mid-layer that can also be worn occasionally next to skin, this is worth checking out, but know that it's not our top recommendation.
Read review: Mountain Hardwear Microchill 2.0
Long Underwear Buying Advice
Safety and comfort in the outdoors become more difficult as temperatures drop or conditions get wet. Your selection of clothing for the activity at hand goes a long way to improving your ability to cope with these situations. This is where a solid layering system comes into play, and the foundation of the modern layering system is next-to-skin long underwear. This appropriately named 'base layer' has arguably the greatest impact on your comfort during active pursuits. It is the only piece that comes in direct contact with the vast majority of your upper body skin. Small defects in design, like chafing stitches or an improper fit, become frustrating agonies during extended use.
A quality base layer needs to be more than comfortable when you're active in the outdoors. An itchy fabric might be annoying, but a product that collects moisture and doesn't keep you warm when wet is potentially life-threatening. It is for this reason that cotton has almost disappeared from technical outdoor apparel. It's a comfortable fabric but provides no insulation when saturated. A wet and cool situation can lead to hypothermia, or worse. The selection of appropriate long underwear is more important than it may initially seem; both for your happiness and health.
Layering for the Outdoors
The principles of modern layering theory rest on the idea that the best way to stay comfortable in an ever-changing environment is to use a system of garments that are layered over one another as conditions or exertion levels change. This typically consists of three pieces of clothing: a foundational base layer to interact with the skin, a middle layer to provide insulation, and an outer shell to protect everything else from wind and precipitation. Like a Russian doll, each subsequent piece is sized a little larger than the last to allow for freedom of movement and the ability to add or shed a layer at will. Other variations exist, such as extra insulating layers for extreme cold. For an in-depth discussion on how to properly layer, be sure to read our three-part layering systems article.
Arguably the most impact-laden layer on your comfort in this system is the base layer. It is there, against your skin, to soothe you or irritate you. Unless you are tanning, it is worn at all times and sometimes for days at a stretch, from sleeping bag to trail to ice climb. Therefore, careful selection based on your own preferences and intended use is important.
Base Layer Weights, AKA Fabric Thickness
Base layers are marketed using several different thicknesses, or weights, categorized into three basic groups; lightweight, midweight, and expedition or heavyweight. Merino wool products almost always list their fabric weight (measured in grams per squared meter). Some manufacturers of blended and synthetic fabrics have also begun publishing the fabric weight, but this system is not yet ubiquitous throughout the market. Thicker products tend to provide more warmth and durability overall. Thinner products are more breathable and dry quicker.
As you cruise the marketplace, you'll find different manufacturers might have different ranges for each weight category. Below, we have listed an average of what we saw listed across the many companies.
The range for lightweight base layers goes from around 100 to 195 g/m². They are thin and typically perfect for shoulder seasons and summer nights. They also perform well during intense physical exertion in cold weather, as breathability often accompanies thin materials. Lightweight tops tend to cost a little less than the thicker stuff, but not a guarantee, and they dry quickly too. You might also encounter silk weight tops on the market, which are even thinner.
Fabric weights between 200 and 295 g/m² are usually considered midweight. When done right, this is the most multi-functional weight. The tops are not for summer, but for chilly spring or fall days and throughout winter, these provide a great foundation for your layering system. They are warmer and more durable than the lightweight models, yet also aim to offer sufficient breathability to keep moisture away from your body.
Expedition or Heavyweight
The thickest long underwear, checking in at 300+ g/m², is called expedition weight or heavyweight for the arduous adventures it is usually associated with. These are shirts intended for viciously cold conditions, but many also work as insulating layers at other times to expand their uses and justify their high price tags. Expect high levels of durability and warmth with this layer, at the price of breathability and drying speed.
Base layers come in three primary constructions: wool, synthetic, and blended material. Choosing between these materials is perhaps the most important choice when deciding on which long underwear to buy.
Merino wool is the fabric of choice for today's premium long underwear. It is composed of fine wool fibers shorn from a fancy breed of sheep. The result is a much softer and less itchy fabric than your old wool holiday sweater. This premium material comes at a premium cost, but these tops are warmer for the weight, breathe better, and dry quickly. Another major advantage of merino wool is its resistance to absorbing odors, which extends the number of wears between washes. Our tests support that wool smells less than synthetics after each wear. Durability is a concern with this delicate material, but for those without student debt or wool allergies, this is the best material you can get.
At a lower price point, many outdoor companies offer synthetic long underwear. This stuff is tough and provides a great value, and its performance continues to creep toward that of merino wool. For the same fabric weight, it is less breathable than merino wool. Synthetics tend to be favored for the thinner weights, not for midweight or heavyweights, offsetting this material's deficiency in breathability and increasing drying speed. Unlike wool, the fibers absorb moisture which leads to bacteria and unpleasant odors over time. It can seem as if these shirts absorb stench that comes back time and again after only wearing briefly. We like these tops for the price conscious or those new to outdoor apparel that may not appreciate the subtle performance benefits wool provides. They are also great when you warmth isn't a major factor.
Over the last several years, hybrids of merino wool, polyester, elastic fabric, and more have been implemented in base layer designs. Manufacturers claim that these products bring together the high warmth to weight ratio, breathability, speedy drying, and odor resistance of wool with the less expensive, more durable synthetic materials. We liked the blended fabric products but didn't find that they totally lived up to their claims. It's a battle of compromises that bridges the gap between wool and synthetics but doesn't necessarily beat them. We continue to keep our eye on this part of the market, though, and hope to see advancements in the coming years.
Finally, there is cotton. You are already familiar with this material as it's the fabric of the ubiquitous t-shirt. This material is inappropriate for outdoor use because it does not insulate when wet. We like this stuff a lot for activities close to civilization but cannot recommend it for backcountry use because of the real risks it poses.
Features and Other Considerations
Base layers are not feature-laden, but there are some features and options to consider before your purchase. Thumbholes built into the sleeve pull the shirt over the back of the hand to increase coverage. This feature is excellent for running in cold weather. It also keeps the sleeves in place when layering up or reaching overhead. Be aware that well-fitting thumb loops are key. Some dig into the skin uncomfortably.
Zip Neck vs. Crew
Most base layers are offered in both crew cut and zip neck options. The advantage of a crew cut is its simplicity, creating a smooth surface to layer under additional tops and jackets. That said, we appreciate the venting versatility of zip neck base layers. The ability to release large amounts of heat when working hard is a huge advantage over crew cuts. The zip neck versions also extend further up the neck, increasing coverage. Lastly, many tops are offered in hooded versions as well. While hoods provide head protection, they get bunched up under other layers when not worn on the head.
Ultraviolet Protection Factor (UPF)
A UPF rating is a measurement of sun protection, and it can be applied to clothing such as long underwear. All shirts protect against sun exposure, yet shirts with additional UPF protection reduce the amount of UV radiation that passes through. The higher the UPF rating, the greater percentage of solar UV radiation is blocked. As tops get wet, worn, and stretched out over time, UV protection decreases. If you are genetically more susceptible to skin cancer risk, a top's UPF rating might be a significant factor for you.
For a deeper discussion of sun protection in apparel, head over to our review of the best Sun Shirts.
The polyester in synthetic clothing is made from oil. Manufacturers like Patagonia and The North Face incorporate varying percentages of recycled polyester in some of their synthetic garments to reduce fossil fuel consumption. We cannot comment on precisely how much oil consumption is reduced by these methods, but we are generally on board with more recycling.
SmartWool and Icebreaker are two manufacturers that claim they receive their wool from sustainable sources. Both companies also advertise "No Museling" wool. Museling is seen by many as a cruel wool harvesting method (and we see their point) in which wool-bearing skin is removed from the backside of the sheep sans anesthetic. The manufacturer tasc asserts that one of their reasons for seeking fabrics from bamboo is to avoid unnecessary chemicals. However, the large amount of chemical solvents used to turn bamboo into smooth fabric questions the sustainability of the process. Verification of these claims and the nuances of individual ethical standards is difficult, but we appreciate the effort of some manufacturers to increase awareness. Learn more about a company's sourcing ethics on their respective websites.
Quality long underwear products need to keep you warm and dry, wick away sweat, be compatible with other layers, and remain cozy and comfy while engaging in physical activity or relaxing at home - and if it looks good, all the better. As usual with recreational gear and equipment, consider your intended uses and environments before snatching up your first/next base layer. We hope we've been able to help you narrow down your choices to a few best matches.
— Ross Robinson