The Best Thermal Underwear to Keep You Warm, Tested and Reviewed
Layer up before the temperatures drop below freezing.
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Once winter comes, layering up is essential. Let's face it: Your new winter coat and cozy sweater just won't cut it when temperatures drop below freezing. That's why cold weather accessories like winter gloves, hats and warm socks are key. And thermal underwear and base layers can make all the difference, whether you're skiing, hiking or just commuting to work.
However, not all thermal underwear is created equal. That's why we've tested some of the most popular and innovative styles to find which truly stand out amongst the rest.
Our top picks:
The Good Housekeeping Institute Textiles Lab has tested all sorts of cold weather gear, from the best winter coats, down jackets and fleece-lined leggings to the best ski gloves and ski goggles in order to find the best products to help keep you warm all winter long. We assess material composition, construction, fit, washability and design to find worthy contenders for our in-Lab and consumer tests. To find the best thermal underwear, we worked with more than 20 consumer testers to try out 31 styles for over 85 days of skiing, snowboarding, hiking and running in cold weather in addition to our in-Lab expert evaluation.
After our top picks, keep reading to learn more about how we test cold-weather gear and what to look for when shopping for thermal underwear and base layers.
Smartwool Classic Thermal Merino Base Layer Crew
Pros
- Soft, cozy merino wool
- Can be worn on its own
- Top scores across the board in tests
Cons
- Requires more TLC than synthetic styles
Whether you're new to merino wool or a devoted fan, Smartwool's merino gear is some of the best around. In our testing, the brand's base layers earned high scores across the board for their soft, cozy feel and quality design. The classic line is the most popular with its versatile midweight construction.
Testers highlighted just how warm and comfortable they felt while wearing the top and bottoms and even struggled to find complaints. One highlighted how everything stayed in place without bunching, and another was shocked at just how warm she felt in windy weather. On top of that, all testers unanimously agreed that the fabric felt softer than other merino wool base layers they owned. The only caveat is that 100% wool garments are prone to shrinking, especially if not taken care of properly, so be sure to follow the care instructions.
| Sizes | XS to XXL |
| Material | Merino Wool |
Pros
- Less shrinkage than other styles
- Warm and comfortable, according to testers
- Moisture-wicking and durable polyester
Cons
- Seams in tights felt irritating to some testers while hiking
This top earned great scores from testers, who lauded its longevity. Several noted that the set shrank less than similar styles they've owned and had a sturdy, midweight feel. One impressed tester said, "I initially thought the base layer was soft and comfortable. That remained true after five days on the mountain."
Tall users (including one 6'4" tester) especially liked how long the arms and torso were, providing coverage down to their gloves and tucking into their pants with ease when snowboarding. However, some testers noted the seams in the tights felt uncomfortable, especially when hiking up more technical trails. That said, this pair outperformed similar sets in all other categories, making it a great option at a fraction of the price.
| Sizes | XS to 3X |
| Material | Polyester, Spandex |
Icebreaker Merino 200 Oasis Long Sleeve Crew
Pros
- Excellent moisture-wicking properties
- Soft fabric with minimal seams
- Great for running and hiking
Cons
- Fabric might be too thin for some
Described as "the ultimate layering piece" by one tester, this popular top from Icebreaker is comfortable and lightweight without compromising on warmth. It's made of luxurious merino wool which naturally regulates temperature, and it performed well in our Lab assessments. Our testers were blown away by the set, appreciating the comfortable fit and feel.
One described it as "super lightweight yet warm" and noted she didn't "feel sweaty when building up a sweat in deep powder." While all of our picks have flat seams to minimize irritation, this top stood out amongst the rest. It has the fewest seams of the bunch, and the ones it does have were the most comfortable. While the lightweight fabric can be worn for a variety of activities, certain colors are a bit see-through, so they cannot be worn on their own.
| Sizes | XS to XL |
| Material | Merino Wool |
Helly-Hansen LIFA Merino Midweight Crew
Pros
- Innovative two-layer design for warmth without overheating
- Great moisture-wicking properties
- High praise from testers
Cons
- Some testers found the seams irritating
Made with two-layer construction, this style from Helly-Hansen features an exterior merino wool shell with an inner polypropylene lining. The inner fabric works to wick moisture away while the wool shell provides warmth. This way, the garment feels lightweight yet warm and easily wicks away any heat to minimize overheating. The set lived up to expectations in our tests: It was one of the few styles in which testers didn't experience any overheating.
Testers called the top comfortable and appreciated the thoughtful technology, noticing how warm it felt without being too bulky. Many even complimented the sleek look and opted to wear it alone after skiing. The only complaints were that the neckline and seams weren't as comfortable as other styles. But testers still gave the set high scores, with one tester describing it as "perfect."
| Sizes | XS to XL |
| Material | Merino Wool, Polypropylene |
Under Armour ColdGear Authentics Leggings
Pros
- Brushed interior
- Thick, stay-in-place waistband
- Offered in three inseams
Cons
- Not the most moisture-wicking in tests
Earning the top spot in our fleece-lined leggings test, this pair from Under Armour is a crowd favorite. It has a smooth, athletic material on the exterior with a brushed inside for warmth and can be worn on its own or under another pair of pants. Not only did this pair keep our testers warm while exercising outdoors, but they also found the soft brushed inner fabric still felt breathable.
On top of that, multiple users highlighted the comfortable yet snug fit and were thrilled that the waistband stayed in place. During in-Lab tests, it proved to be durable, earning high scores for pilling and shrinkage. While this pair didn't wick moisture as well as others we tested, it still earned a respectable score in our moisture-wicking test.
| Sizes | XXS (Short) to XXL (Tall) |
| Material | Polyester, Elastane |
Kari Traa Rose Half-Zip Top
Pros
- Snug, glove-like fit
- Fun colors and patterns
- Cozy merino wool with stretchy knit panels
Cons
- Too warm for some testers
- Only available in women's styles
While most thermal underwear comes in solid colors, Kari Traa stands out for its Nordic-inspired patterns. In fact, several testers highlighted the fun design, calling it "cute" and "stylish" enough to wear on its own after a day of skiing. Beyond its distinct look, the zip-up top and high-waisted bottoms have lightweight, knit panels for added stretch and mobility.
The merino wool fabric also kept our testers warmer than other base layers they've worn while skiing, with several opting to forego a mid-layer. That said, those in warmer skiing conditions found it too warm. Many testers told us they liked everything about the set, from the cozy fabric to the glove-like fit, with one sharing, "I loved these base layers, so much. I ended up washing them almost every day, so I could wear them again the next day and went to buy more as soon as I got home."
| Sizes | XS to XL |
| Material | Merino Wool |
Columbia Omni-Heat Infinity Baselayer Tights
Pros
- High scores in moisture-wicking tests
- Thermal reflective lining
- Lightweight yet warm
Cons
- Ran small for taller testers in evaluations
It may look unassuming, but this lightweight pair of tights earned the spot as the warmest thermal underwear on our list. The secret? It's got a thermal-reflective lining that's designed to help retain body heat without weighing you down. In fact, one tester even said, "I did not have to wear any mid-layer between these and my regular snowboard pants in order to stay warm, even in very cold temperatures."
Others agreed, sharing how impressed they were with the warmth these tights (and the matching top) provided, even in extremely cold temperatures. Beyond that, they excelled in our moisture-wicking tests. Another tester even told us, "They really did keep me warm while also being relatively breathable." Taller testers often had to size up for a better fit.
| Sizes | XS to XXL |
| Material | Polyester, Elastane |
Pros
- Plush fleece lining
- Breathable yet cozy
- Airy and stretchy
Cons
- Too thick for those who prefer lightweight merino wool
Lined with a lofty fleece material, Patagonia's Capilene fabric is popular among hikers, including some at GH who wear it year-round. In certain climates, it can even act as an all-in-one base and mid-layer. Testers were pleased by the unique material, calling the simultaneous breathability and warmth "outstanding." One described it as the "perfect balance between coziness and freedom of movement" and found herself reaching for the top for everything from skiing and running to lounging indoors.
Beyond its crowd-pleasing fabric, it proved moisture-wicking in our tests. Plus, some testers noted the tops and bottoms moved with them rather than restricting their movements. The caveat is that the lofty fleece isn't for everyone. Those who prefer merino wool will likely find it too thick and bulky, especially for skiing, but if you've never loved the feel of a wool base layer, it might be the perfect alternative.
| Sizes | XXS to XXL |
| Material | Polyester |
Uniqlo HEATTECH Ultra Warm Crew Neck Long-Sleeve T-Shirt
Pros
- Great for layering with sweaters
- Brushed inner lining for extra coziness
- Not too bulky
Cons
- Not warm enough for cold weather sports
On colder days in the winter, a good coat and cozy sweater might not be enough to keep you warm when out and about. This top combines soft brushed fabric with Uniqlo's signature HEATTECH technology, which the brand says "wicks the body’s moisture into fibers and converts the kinetic energy into heat." In fact, it's a bit thicker than the brand's classic thermal underwear thanks to the brushed lining, which, according to Uniqlo, makes it 2.25 times warmer.
While our testers found this style stretchy and cozy, they noted it felt better for everyday wear, rather than skiing or hiking, and constantly reached for it when commuting to the office. Still, Uniqlo's offerings were highly praised, with one tester saying, "They check all the boxes for what I want my base layers to be like. They’re comfortable, lightweight, warm and breathable."
| Sizes | XXS to XXL |
| Material | Acrylic, Polyester, Rayon, Spandex |
Outdoor Research Alpine Onset Crew
Pros
- Top scores in Lab tests
- Comfortable waistband
- Lightweight yet warm
Cons
- Not all testers liked the thin, lightweight nature
Outscoring all other styles we tested in our moisture-wicking tests, this top will keep you dry during all kinds of cold weather activities. It's made of a blend of merino wool and recycled polyester and it proved to be not only moisture-wicking but also temperature-regulating. In fact, our testers gave it perfect scores in both categories after several days out on the slopes.
One tester who tried the full set shared, "[I wasn't] sure if they would be warm enough given how lightweight they felt, but they were perfect." Others called the waistband "soft" and praised the snug yet comfortable fit, noting it didn't dig in like similar thermal underwear they've tried. The fabric is thin and lightweight, acting as a next-to-skin layer rather than a more midweight option.
| Sizes | XS to XL |
| Material | Merino Wool, Polyester |
How we test thermal underwear
The Good Housekeeping Institute Textiles Lab routinely evaluates all kinds of cold weather gear, from winter coats and down jackets to heated gloves and warm socks to find the best of the best. We begin the process by researching popular styles online, taking into account everything from materials to design and construction. Using our categorical expertise, we narrow down the top contenders from hundreds of products for hands-on testing.
In the Lab, we conducted an in-depth design assessment, taking note of the texture of the fabric and the construction, including any seams and gussets. We also repeatedly laundered each product before performing moisture-wicking testing and checking for notable shrinkage. Select styles were further assessed for pilling resistance and stretch recovery.
Beyond our in-Lab tests, we worked with more than 20 consumer testers to try out thermal underwear in their daily lives. All of our testers wore these base layers while skiing or snowboarding and several tested them while hiking or running outside in cold weather. Some also wore them on their daily commutes in the windy northeast and midwest.
In all, we tested 31 different styles of thermal underwear, before analyzing Lab and consumer testing data to find the best available.
Things to keep in mind when shopping for thermal underwear
✔️ Material: Cotton is one of the most popular materials in the world, but when it comes to keeping you warm, it's not the best, especially for winter sports. It holds onto moisture rather than wicking it away from your body which can cause you to feel sweaty. Instead, opt for a material like wool, which is naturally temperature-regulating and respectably moisture-wicking. Fleece is also a great option for insulation, especially when it's made from polyester, which is known for its excellent moisture-wicking properties. Make sure the styles you're interested in also have some spandex or elastane for both a snug fit and added stretch.
✔️ Seams: Look inside the garment to ensure the seams are flat rather than raised. Flat seams are ideal when sweat and movement are involved. They can help prevent or minimize chafing and irritation.
✔️ Gusset: For bottoms, check the crotch for an extra piece of fabric (often triangular or diamond-shaped) that's sewn in. Having a gusset prevents the leggings or tights from riding up with movement. If a pair only has seams at the crotch, it's not ideal for physical activity and may feel uncomfortable.
✔️ Stretch/Compression: To ensure a comfortable level of stretch and compression, you'll need to try the garment on. If you know you’ll be running, try moving your legs to mimic the movement of your strides. If you’ll be skiing or snowboarding, try moving around in a few positions you'll likely find yourself in on the slopes.
✔️ Moisture Wicking Capabilities: Even though most activewear claims to be moisture-wicking, it can be difficult to predict how fabrics will manage your sweat before wear. If you're uncertain, try this mini-version of our test: Place a small drop of water on the inside of the fabric; it should absorb quickly and spread out wide. If it just absorbs, that’s a sign the fabric will stay wet with sweat. Fabric that doesn't wick moisture well tends to feel hot during exercise.
✔️ Waistband: Most bottoms have waistbands that use elastic bands to stay in place, but not all do. Some bands are thin, while others are wider. While the best waistband style is a matter of preference, our testers found it more comfortable to tuck their tops into their bottoms (to prevent cold air from sneaking in) and preferred a thicker waistband.
Why trust Good Housekeeping?
Grace Wu is a textiles product analyst at the Good Housekeeping Institute who oversaw recent thermal underwear and base layer testing. She's written stories about all sorts of winter accessories, including heated gloves and warm socks. Prior to joining GH, Grace earned a Master of Engineering in Materials Science & Engineering and a Bachelor of Science in Fiber Science from Cornell University.
Grace Wu (she/her) is a product reviews analyst at the Good Housekeeping Institute's Textiles, Paper and Apparel Lab, where she evaluates fabric-based products using specialized equipment and consumer tester data. Prior to starting at Good Housekeeping in 2022, she earned a master of engineering in materials science and engineering and a bachelor of science in fiber science from Cornell University. While earning her degrees, Grace worked in research laboratories for smart textiles and nanotechnology and held internships at Open Style Lab and Rent the Runway.
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