The Best Thermal Underwear of 2024 for Men
It’s easy to let low temperatures and bad winter weather keep you locked indoors, but the right layering means you don’t have to freeze to stay outdoors through colder months. Like any good base layer, the best thermal underwear for men helps transport moisture away from the body and out of your layers. Getting soaked with sweat is a sure-fire way to be really cold, so make sure you wear just enough on top of your thermals to avoid overheating.
In addition to moisture transport, these base layers help keep some of your body’s heat close, so you don’t have to bundle up like that kid in A Christmas Story just to go outside. Keeping layers to a minimum makes you more mobile, whether you’re out for a run, chopping firewood, or just walking in a winter wonderland.
Men don thermal underwear for as many reasons as they have to go outside in winter, so we’ve shared our favorites in a range of categories to pinpoint your perfect set.
Best Overall Men's Thermal Underwear: Artilect Boulder Crew Top and Leggings
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Both merino wool and synthetics have had their day as the base layer of choice. Recent innovations blending the two, such as Artilect’s Boulder 125 base layers, have managed to capture the best qualities of both. The bulk (85 percent) of the Nuyarn merino fabric is odor bacteria-suppressing wool, but the nylon gives it great stretch without feeling like spandex. The inside is also incredibly soft to the touch and flatlock seams aren’t noticed at all. The fit is athletic, making this base layer set an option for pretty much any winter activity and maximizing moisture transport. This 125-weight set is the lighter of two Artilect thermal sets. Their 185-weight is appropriate for the coldest temperatures and lower-intensity activities outside, but the 125s should be plenty for most people and are definitely the right choice for high-output sports such as running and backcountry ski touring.
Materials: 85% merino wool, 15% nylon
Colors: Black, Kalamata/Ash, Dusk Blue/Black
Sizes: S–XXL
Related: The Best Camping Showers and Washing Gear for Keeping Clean on Adventures
Best Merino Wool Men's Thermal Underwear: Ibex Woolies Zip Top and Bottoms
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We love the feel of modern merino apparel against the skin, but our only gripe has been that the garments tend to stretch out over years of hard use and can wear faster than seemingly indestructible synthetics. This update to Ibex’s popular Woolies base layer uses a Nuyarn merino blend fabric similar to our top overall pick from Artilect. The difference here is a slightly more relaxed fit than Artilect’s athlete-minded tailored cut and more stylish color options. The result is a cozy yet functional set of thermals that you can wear day after day without worrying about synthetic stink or premature wear. Ibex makes a crew neck long-sleeve in addition to the ? zip top, but the extra-wide neck on the crew isn’t our favorite. We’d recommend the zip unless you like that muumuu neck cut for your base layer tops.
Materials: 85% merino, 15% nylon
Colors: Black Gray Stripe, Lake Effect, Olive Drab, Black
Sizes: S–XXL
Best Value Men's Thermal Underwear: Hot Chillys Pepper Top and Bottoms
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In the '80s, Hot Chillys was one of the first companies to popularize form-fitting, moisture-wicking thermals for active pursuits such as skiing. Their lineup has evolved with the times, and while they make plenty of higher-end pieces, the Pepper line delivers great value with a fully synthetic mid-weight layer that’s a great all-around set for any outdoor endeavor. The fit is relaxed so it might not meet the demands of high-intensity winter sports, but it’s a great all-around thermal for staying warm outside in a range of activities. The Pepper has a double-layer construction that helps retain warmth close to your body but efficiently transports moisture away from the body to keep you dry.
Materials: 100% polyester
Colors: Black
Sizes: S–XXL
Best Men's Thermal Underwear for Skiing: Obermeyer UltraGear Zip Top and Bottoms
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Keeping your core warm while skiing is the best way to help avoid cold hands and feet—the main reason people cut an epic ski day short. For warm, sunny spring skiing, almost any light thermals will do, but for dark January powder days on the chairlift, Obermeyer’s fleece mid-weight UltraGear layers are perfect for adding breathable warmth under weatherproof ski shells and pants. Some people fear the cold and rock insulated jackets and pants skiing, but we prefer Gore-Tex shell outerwear that lets us adjust our under layers to the weather. These UltraGear layers are usually enough on their own, but for the coldest days, they have a relaxed enough fit to be worn as fleece mid-layers with lighter, tight-fitting base layers underneath.
Materials: 92% polyester, 8% elastane
Colors: Black, Knightly
Sizes: XS–XXL
Related: 5 Intense Workouts to Build Stronger Shoulders
Best Men's Thermal Underwear for Biking: Pearl Izumi Quest Jersey and Bib Tights
Justin Park
Dressing for cold-weather biking can be tough. On the one hand, you’re usually generating a ton of body heat, which can easily lead to soggy layers within a few minutes on the road or trail. On the other, you’re often fighting cold hands and feet and riding fast and into wind, which can chill you quickly. When it’s cold and we're pedaling, we like to pair heavy gloves and shoe covers with warm but highly breathable base layers and wind-blocking jacket and pants when necessary. The Pearl Izumi Thermal Bib Tights pair a mid-weight, highly stretchy fleece material on the legs with a thin, breathable upper and a built-in chamois pad, so you don’t have to squeeze a layer underneath. There are very few seams to irritate your skin and the legs fit snug, so you get maximum moisture transport when you’re grunting out a climb, with zero material flapping around that might catch in your gears. The Quest Thermal Jersey isn’t quite as form fitting, so it helps retain body heat and has a full-length zipper if you need to shed steam fast to avoid getting sweaty.
Materials: 100% polyester
Colors: Black
Sizes: S–XXL
Best Men's Thermal Underwear for Warmth: Hot Chillys La Monta?a Zip Top and Bottoms
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Sometimes winter conditions can be extreme and they call for extreme warmth, even in your base layers. Whether you’re trying to hold out all morning in a deer stand, watching a football game with your butt on aluminum bleachers, or just out for a walk in subzero temps, Hot Chillys La Monta?a base layers are about as warm as thermals get before they become something else. While they can be worn as an insulating mid-layer, the fit is snug enough to function as a next-to-skin layer despite their thicker fleece construction. These are the most heavyweight thermals Hot Chillys makes, but they’re still pretty light, achieving their warmth via lofted polyester fibers that trap warm air near the body while letting moisture escape. These are a heavy option and we don’t reach for them lightly. Here's what you pull out when you’re worried there isn’t enough insulation in your entire house to keep you warm outside.
Materials: 100% polyester
Colors: Black
Sizes: S–XXL
Best Men's Thermal Underwear for Comfort: Kora Bamboo Top and Bottoms
Justin Park
While we wear both natural and synthetic base layers, we’ll admit to preferring the feel of natural materials such as merino wool to slick, stretchy spandex. Kora, a cottage producer of mostly yak wool outdoor apparel, surprised us with their incredibly soft and warm bamboo base layers. This thermal set has a jersey cotton-like feel against the skin and the contoured but not tight fit makes them the most comfortable thermals we own. Despite the comfort, these are still performance base layers that are a great choice for anything from snow blowing to skiing, yet are comfortable enough that we find ourselves wearing them around the house like holiday pajamas.
Materials: 90% bamboo, 10% spandex
Colors: Deep Purple, Cerise Red, Dusty Blue, Earth Green, Ecru, Soft Black
Sizes: S–XXL
More Men's Thermal Underwear We Love
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Smartwool is an industry standard for a reason. Of all the thermal garments we’ve tested, Smartwool’s All-Season Base Layer line is the most versatile. The 150-weight feels like what a base layer should be: It’s not your primary insulation, but there to keep you from losing your heat—or your cool. From cold dewy break camps and hiking in the heat, to bartending events amid a sweltering crowd (on the same day), the All-Season line kept true to its name and kept us warm enough in the cold, cool enough in the heat, and stylish all throughout. However, the line isn’t without its particulars. Being an all-purpose outdoor base layer, the line favors a slim fit, with slender arms. With 12 percent nylon, the tops have the stretch to accommodate broad chests, but those with larger biceps may need to size up. Likewise, for bottoms, while those with tree trunk thighs can still sport medium boxer briefs, they will roll up under jeans and fitted pants. For long bottoms, thick thighs demand a large. Luckily, Smartwool’s waistband, the thickest of and toughest of those tested, is also accommodating for a range of waist sizes.
- Materials: 88% merino wool, 12% nylon
- Colors: Pewter Blue Wash, Laguna Blue-Deep Navy, Honey Gold, Fox Brown, Black, Fern Green, Iron Heather
- Sizes: S–XXL
Justin Park
Compression apparel has its roots in medical applications (remember grandma’s putty-colored stockings?) and so do the thermals from German apparel company CEP, which makes serious compression socks and base layers for athletes. We wore their suction-fit and very warm base layers for resort skiing last season and appreciated how warm they were and how well they layered under other ski clothes. There are some potential performance benefits to compression gear conferred through improved circulation and the skin suit fit is snug without feeling restrictive. The tight fit also definitely helps with moisture-wicking since there’s no airspace for sweat to get trapped between skin and base layer. The ? length on the bottoms was also appreciated when wearing ski boots or any other calf-high winter footwear.
- Materials: Varying amounts of polyester, polyamide, modal, merino wool, and spandex
- Colors: Royal Blue, Navy, Black, Orange
- Sizes: S–XXL
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Decathlon is always a dark horse for budget outdoor gear. Their base layers are no exception. Decathlon’s offerings are the only ones here to tailor the blend featured in every item to performance, instead of having a largely across-the-board blend makeup. Their ? zip top features a softer, more synthetic liner both around the neck and behind the zipper, for a softer feel around your neck that prevents skin contact with a cold zipper. Behind the knees of the long bottoms is a synthetic-heavier blend for better breathability and to prevent fabric bunching. However, Decathlon favors a smaller, less slim-cut fit. For broader chested and thighed individuals, this makes it a necessity to upsize to options that are longer and looser than most other base layers. Nevertheless, for those who are willing to trade ease of sizing for an excellent deal, thoughtful engineering, and supple feel, Decathlon’s offerings provide a great bang for your buck.
- Materials: Varying amounts of wool, polyamide, elastane, and acrylic
- Colors: Black, Asphalt Blue
- Sizes: S–XXL
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Although they're medium-weight, REI’s 100-percent merino base layers were easily one of the warmest collections we tested. Despite REI’s middle-of-the-pack price range, this makes it one of the best deals for cool weather. Having less stretch and durability than blends with synthetic/merino blends, they did show slightly more wear over time. To overcome the lesser stretch, REI favors a slightly more relaxed (and short) fit. All but the thickest thighs will fit into the medium bottoms. The full merino tops weren’t quite as soft as our next contender, but given their thickness and moderate stretch, didn’t rub our skin so much as hug it—while providing arguably some of the best pit stink prevention. For cold-weather adventures or cold-blooded people, they offer excellent value, great comfort and scent control, and good versatility.
- Materials: 100% merino wool
- Colors: Balsam Teal, Black, Cabin Wood, Desert Moss, Mountains Falcon Brown, Sargasso Sea
- Sizes: S–XXXL
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These thermals are so unique, they pretty much live in a category of their own. Made from polyester, silk, metals(!), and elastane, there’s really nothing like these ultrathin, ultra-breathable base layers ideal for high-intensity winter sports. For sports such as ski touring and nordic skiing, the short-sleeve top and ? length bottoms leave plenty of skin surface area bare for releasing body moisture. Pick up the garments and you’ll think they’re an infant’s until you slip them on and they easily expand to your body’s form. There are only two sizes because the Silk Reflects are so expandable. This gear isn’t adding much warmth, but it provides the most minimal possible layer between you and your outerwear when staying cool and dry is your number one priority.
- Materials: 69% polyester, 25% silk, 3% metal, 3% elastane
- Colors: Cloud
- Sizes: S, L
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There are lots of henley-style thermals you can buy, but most of them are cotton-based, making them impractical for much more than taking holiday photos by the fireplace. Le Bent specializes in technical base layers for outdoor sports and their Tech Henley is one of the few we’ve found that pairs the casual style of a henley with performance fabrics. We won’t claim that the signature buttons of the henley will translate into some kind of performance benefits, but it looks a lot more stylish when you head straight from the slopes to an après get-together. Their Core Base Layer Bottoms use the same performance blend of polyester, wool, and a grab-bag of bamboo-based rayon, cashmere, and other materials for a stretchy, plush feel against your skin.
- Materials: 44% polyester, 29% lyocell, 8% polyamide, 8% wool, 6% spandex, 5% cashmere
- Colors: Dark Cloud
- Sizes: S–XL
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One-piece thermal underwear isn’t as common as it once was, but Airblaster keeps the pajama-style fun alive with their beloved Ninja Suit, now made with merino wool (the Classic Ninja suit is a polyester/lycra blend). The best thing about the Ninja Suit is that it frees your waistline from excess materials and prevents your bottoms from riding low and your top from inching up which can leave your core chilly. They also make an outerwear-style Ninja Suit Pro that adds water resistance to key areas, so you can go outside wearing nothing but your Ninja Suit. And, yes, there is a 350-degree “trap door” to make bathroom breaks less complicated.
- Materials: 55% merino, 37% Tencel, 8% spandex
- Colors: Black, Oxide, Sweetin Resin
- Sizes: XS–XXL
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Why You Should Trust Us
Where Justin Park lives at 10,000 feet in Colorado’s Rocky Mountains, winter lasts more than half the year, giving him plenty of time outside wearing base layers. From shoulder seasons mountain biking in cool weather to backcountry hunting to skiing in sub-freezing temperatures and working outside, he gets more days in thermal underwear than not. He tests base layers from outdoor apparel brands throughout the year. For this article, he specifically tested a dozen additional men's thermals to find the best of the best for different applications—evaluating primarily for warmth, breathability, and comfort.
Ian Graber-Stiehl writes about gear and the outdoors for over two dozen publications across the web and newsstands. He's also an outdoorsman, angler, bikepacker, and knife obsessive who's also usually the designated camp cook and bartender—including during the colder months.
Related: This Is the Best Ski Gear We Tested for 2024
What to Look for in Thermal Underwear
Weight
You can find a wide range of weights when shopping for thermals, and how you intend to use them should dictate how heavy you go. For high-output activities such as cross-country skiing, running, and biking, lighter weights are usually better unless you’re out in extreme cold. For light-duty applications such as walking or simply taking in a late-season football game, look for a heavyweight thermal. While some companies will list numeric fabric weights for their products, it’s hard to translate those numbers into the reality of how warm a particular thermal will feel, so it’s best to go by the description of the weight. Companies will often offer multiple weights, usually lightweight, midweight, and heavyweight, and those are good guidelines for understanding the warmth you can expect from a particular set.
Materials
There are two broad categories of materials used (and often mixed) when companies are constructing their thermals: natural and synthetic. Synthetics such as polyester and nylon are long-lasting and provide good stretch in base layers but can retain body odors. Natural fibers such as merino wool have natural antimicrobial properties and do a better job retaining body heat but usually aren’t as durable and may stretch out more easily over time. Elastane, sometimes called by trade names Lycra or Spandex, is often added in smaller quantities to give thermals additional stretch. You can compare the elastane content to get an idea of how stretchy a product might be, but modern techniques have made excellent stretch possible with new blends of wool, nylon, and polyester as well. Some garments, including two featured below, use bamboo fiber, which can be synthesized into a form of rayon.
Related: The Best Men's Winter Boots for 2024
Fit
A performance base layer should be form-fitting to maximize its ability to move moisture away from your body. Most people assume thermals are only there to keep you warm, but while they do help retain some body heat, their primary function is moisture transport and a baggy thermal doesn’t do that job very well. If you prefer a looser, more comfortable fit, there are plenty of options that you don’t have to fight to put on. But no matter your preferences, having thermals that sag and bunch not only hurt moisture transport, but it can also affect comfort when you add layers on top.
Related: The Best Men's Winter Gloves for 2024
Why You Should Consider Merino Wool Thermal Underwear
Whether you’re hitting the trail or the town, you shouldn’t have to haul extra clothes or plan your day around a laundromat run to keep people from being able to smell where you’ve been. Enter merino wool, a superfine wool from Merino sheep. With smaller diameter fibers, it feels much softer on the skin and dries considerably faster than traditional wool or cotton. It doesn’t air out quite as quickly as nylon or polyester, but is full of air pockets that allow it to absorb up to 30 percent of its weight in moisture before feeling wet—compared to around 5 percent for many synthetic fibers. When combined with the fiber’s thin diameter, it makes for a fabric that is lightweight, sweat-wicking, breathable, and insulative even when moist.
Simply put, merino can keep you warmer in the cold and cooler in the heat, with toughness that makes it an increasingly popular option for military garments—and natural antimicrobial properties that make it possible to stretch fewer items over more adventures, with less stink. Here’s our take on the market’s best options.
Related: These Are the 12 Best Sweaters for Men
Top Tips for Picking Merino Wool Thermal Underwear
Merino is much softer than traditional wool, but not quite on par with cotton. If possible, try merino garments on in a store to get a feel for the fabric.
Merino doesn’t have the stretch or durability of some synthetic fabrics. It’s often blended with other fabrics like nylon, polyester, and Tencel. Knowing the properties of these fabrics can help you get a handle on how the blend will perform.
From a few inches away, you’d be hard-pressed to pick up a scent from most merino garments after wearing them for a day or so. However, bury your nose into the bottom half’s backside or hunt for an odor in the pits of pestilence, and you’ll find one. Airing out clothes overnight—especially if you take a minute to wash the pits prior, will keep them truly scent-free for days.
Merino can be washed on warm, and dried on either low or without heat. However, if you hang tops to air dry, either do so on a rounded hanger, rack, or portable line like the Sea to Summit’s Lite Line Clothesline. Wool has a memory, and the pointed edges of some hangers will leave shirt shoulders with unsightly bumps.
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