The Best Thermal Underwear of 2023, Tested and Reviewed

The incredibly comfortable Kari Traa Rose Wool Base Layers top our list for winter warmth.

Jump to a Section

We independently evaluate all recommended products and services. If you click on links we provide, we may receive compensation. Learn more.

Travel + Leisure / Anna Popp

When temperatures drop, many of us tend to head indoors until spring. But for those of us who enjoy outdoor activities like skiing, snowboarding, hiking, and even just walking, some bundling up is in order. The perfect cold-weather outfit is all about proper layering, so starting off with a solid base in the form of great thermal underwear is a must.

Thermal underwear is the comfy, breathable, and usually form-fitting two-piece set you wear under heavier apparel like ski pants, parkas, and jeans to stay extra warm. They can even be worn on their own for neighborhood jogs or walks with the dog before the mercury has fully plummeted. To find the very best thermal underwear options on the market, Travel + Leisure editors personally tested dozens of sets, including our overall favorite, the breathable and stylish Kari Traa Rose Wool Base Layer. While our best overall base layer is only available for women, there's certainly a lot to love about our runner-up, the incredibly comfortable Odlo Performance Wool Warm Base Layer, which comes in men's sizes. Lightweight base layers, budget picks, and the best thermal underwear for everyday wear also made our list.

Amazon

Why We Love It: In addition to the top-tier athletic performance, they’re sleek, figure-flattering, and come in fun wintry prints.

What to Consider: They’re only available in women's sizes.

This half-zip turtleneck top and curve-enhancing bottoms will never fail to make you look good, and, more importantly, you’ll always feel good wearing them. Skiers, mountaineers, and snowshoers have long adored merino wool for its natural temperature-regulating, moisture-wicking, and odor-resistant properties, so it comes as no surprise that Olympic gold-medalist Kari Traa's signature garments are made entirely from the material. Four-way stretch ensures they won't hinder mobility, and the soft feel makes them a great wardrobe choice for cozying up next to the fireplace.

We get it — patterned thermals aren't for everyone. But the snowflake design inspired by Traa's native Norway is so cute yet subtle it's hard to resist dropping them in your cart. The set comes in alpine-chic colors ranging from taupe to royal blue, all accented by stitching and flattering side panels that help it achieve a close-to-the-body fit for easy layering. The half-zip neckline adds another polished touch, and it allows you to increase airflow after working up a sweat in the slightly compressing set.

"I love how breathable these feel despite their warmth," our tester said. "Even in my New York City apartment with a sweltering radiator, I didn't feel like I was suffocating. Everything from the smooth, sturdy zipper to the seams felt thoughtfully made. I think they'll last for many wears throughout the season and many seasons after that. If you plan on doing rigorous activity in the winter, these are a great choice — I got multiple pairs and wore them three days in a row on my first ski trip of the year."

Price at time of publish: $120

The Details: S-XL | Merino wool

Travel + leisure / Lydia Price

Wild Rye

Why We Love It: They hug curves, muscles, and everything in between just right.

What to Consider: We think the cuffs feel a bit baggy.

Available for women in sizes 0 to 18, these thermals were designed for every female athlete — amateur and otherwise — to find the perfect fit. The 100 percent merino wool top and matching bottoms feel soft and cozy, moving with the body during winter sports without digging in anywhere, plus handle sweat like champs. We found the fabric warm enough to wear as a standalone on milder days, which gave us a chance to show off the vibrant print, and a zipped neckline is at the ready when you need to cool off.

"I really worked up a sweat in these but felt warm and comfortable the whole time," our tester said. "Sometimes I find myself cringing through an after-ski drink or snack because I feel soggy and cold, but I hung out in these for quite a bit feeling great."

Price at time of publish: $129

The Details: 0-18 | Merino wool

Travel + Leisure / Lydia Price

ODLO

Why We Love It: They’re just as warm and breathable as they are stylish.

What to Consider: The colors are very limited.

"These layers fit like a second skin," our tester raved about these Odlo thermals. Available for both men and women, they check all the boxes for a great pair of base layers. Not only do the top and bottom boast the perfect fit (not too tight, not too loose), but they’re also ultra-warm, breathable, and extremely stylish thanks to a subtle angular pattern found in all the available colors. Speaking of colors, women can snag this set in black or winetasting, while men have a choice between black, grey, and an ocean-inspired blue. No matter the hue you choose, you’ll enjoy the natural thermoregulation and moisture-wicking technology of a soft merino wool, polyester, polyamide, and elastane blend.

"I have other wool base layers from Ibex, Smartwool, and Icebreaker; these are as good if not better, and have a nice stretch without feeling constricting. I like the deep jewel-toned colors and the pattern, and love the fit. I will live in these this winter," our tester shared.

Price at time of publish: $100 for bottom

The Details: XS-XL | Merino wool, polyester, polyamide, elastane

Travel + Leisure / Frances Crouter

Amazon

Why We Love It: They’re extremely soft and cozy.

What to Consider: They’re made of cotton, which isn't good at managing moisture, so you shouldn't wear them for active pursuits.

Are you all about simplicity? Opt for this Pisiqi set. Unlike many of the picks on our list, this one features a top and bottom that come together and are available in nine colors. Though they’re crafted with 100 percent cotton and offer a roomy fit, which makes them perfect for casual wear. You’re sure to stay warm and toasty whether you wear them as a base layer or alone. Keep in mind that because these are made of cotton, they shouldn't be worn for occasions that'll involve sweat or other moisture. But if you want a budget-friendly way to stay cozy day-to-day, these are perfect.

"I wore these outside for a walk in 35-degree weather and the material didn't feel wet or super cold when I got back home," our tester said. "They’re super soft, stretchy, and comfy, and they keep you warm but not too hot. Even after washing these, they’re still intact with no tearing or string peeling. They’re still super stretchy with no shrinkage."

Price at time of publish: $40

The Details: XS-XXL | Cotton

Carhartt

Why We Love It: They’re available in regular, tall, and big sizes.

What to Consider: They’re not very compressive.

There's plenty to love about these reasonably priced thermals from workwear brand Carhartt: They’re lightweight, sweat-wicking, and warm enough to wear without much else overtop. We’re also impressed by added features like thumb loops on the sleeves, odor-fighting properties, anti-chafing seams, and even tagless labels on the pants for added comfort. Their most redeeming quality, though? They’ll keep you from freezing or overheating in all types of weather, activities, and regions.

"These are very warm," our tester said. "I was able to snowboard with the thermals and just a shell in 30-degree weather. The top was warmer than a T-shirt and hoodie combo as well when walking around a windy backyard during a brisk California night. I have owned many expensive base layers and these are as warm as or warmer than most of them."

Price at time of publish: $40 for top, $40 for bottom

The Details: S-4XL, including regular, tall, and big sizes | Polyester

Under Armour

Why We Love It: They’re super sleek, yet toasty as can be.

What to Consider: The neck and arm holes are pretty tight.

If you want warm, Under Armour's ColdGear 3.0 set has warm. The thermals trap body heat to warm your skin quickly and thoroughly, but you don't have to worry about overheating or sweating, since temperature-regulating technology wicks moisture and provides breathability. Happen to wipe out in the snow or get caught in the rain? No worries — both the top and matching leggings dry quickly and eliminate odors. On top of all that, they’re super comfy.

"These did a GREAT job of keeping me warm and dry," our tester shared. "I would trust these in very cold conditions, including those where I sweat a lot (like cross-country skiing) to keep me dry. The fabric feels like it has a very tight, high-quality weave. They were also great around the house — I wore them in my home office where I normally have to use a space heater or a blanket, but that day I was warm enough [that] I didn't need one!"

Price at time of publish: $70 for top, $70 for bottom

The Details: XS-XXL for top, XS-XL for bottom | Polyester, elasterell

Amazon

Why We Love It: They’re waterproof — and they just look really cool.

What to Consider: They’re not the warmest option on our list.

There's something about a clean, crisp side stripe that makes you look and feel uber athletic — and that's only one of the many reasons we’re obsessed with this set from Helly Hansen. The matching top and bottom are also comfy, waterproof, breathable, and extremely lightweight. Choose a top in one of 11 colors and seven sizes, then pick a bottom in one of three colors and five sizes. Women's sizes are also up for grabs.

"The Lifa material feels more durable compared to merino and typical base layers," our tester said. "That said, these are not super warm, but they're not supposed to be. Are they the base layer for sitting on the lift in the Rockies when it's 0 degrees? No. Are they the base layer for spring conditions or for high-output activities like ski touring? Yes, I think so. Plus, they’re higher performing than others I've used and should last for seasons."

Price at time of publish: $44

The Details: XS-3XL for top, XS-XXL for bottom | Polypropylene

Arc'teryx

Why We Love It: They’re soft, warm, and made with several barely-noticeable pockets.

What to Consider: The fit is boxy.

Equipped with a lightweight construction, breathable feel, and a fun, futuristic vibe, these layers from Arc'teryx take comfort to a whole new level. "This set is so cozy and soft on the inside," our tester shared. "I throw on the pants every day when I work from home because they have the same comfort of sweatpants, but they look like thick leggings so they're super versatile for leaving the house." The quarter-zip top is equally lightweight and cozy as the bottoms and the inside fleece lining is incredibly soft and warm. There's virtually nothing you can't do in these thermals thanks to their temperature-regulating capabilities and durable weave, so you can feel confident about packing them on all types of trips. We especially love that the top's subtle turtleneck and half-zip lock in warmth, while the bottom's thigh pocket efficiently holds and protects your smartphone. Arc'teryx also makes a men's version.

"I've definitely broken out in sweat while wearing this set and I've never felt damp, so I think it does a good job of wicking the moisture and not absorbing it," our tester said. "The top and bottom [are pricey], but it's worth it for people who ski or spend a lot of time outdoors in the winter."

The Details: XS-XL | Nylon, polyester, elastane

Travel + Leisure / Anna Popp

Marmot

Why We Love It: In addition to offering extra sun protection, these base layers have top-tier sweat-wicking abilities.

What to Consider: There was some pilling at the wrists after several wears.

Loaded with UPF 50, this set is perfect to wear by itself during milder days, but it's form-fitting enough for easy layering when things get chilly. The inside is a soft and thin fleece-like material that feels great against the skin, and the exterior is smooth to the touch. We think both the top and bottoms have just the right amount of stretch to avoid feeling constrictive. Our tester also raved about the Polartec material's moisture-wicking ability and appreciated the zipper and thumbholes for temperature management. The one downside is that there was some pilling along the shirt's cuffs after several wears. Still, we think these base layers' impeccable sweat-wicking, added sun protection, and perfect amount of stretch make them worth considering.

"It's great to have a thin warm shirt like this to throw on, even when I'm not doing outdoor activities. I've worn these in a variety of different temperatures while skiing and have never felt either cold or not ventilated properly," our tester shared.

Price at time of publish: $99

The Details: XS-XL | Polartec

Travel + Leisure / Lydia Price

Patagonia

Why We Love It: They’re stylish enough to wear anywhere, and they’ll keep you from sweating.

What to Consider: The neckline is high and may bother some shoppers.

If you’ve been looking for the perfect layer you can wear on the slopes, around the house, and out and about, Patagonia's Capilene Air thermals are here to end your search. The lightweight, sweater-like top can be comfortably worn under pretty much anything or on its own, while the bottoms are so soft and comfy, you may just want to wear them to the gym or even to bed. Both pieces are also extremely breathable, so forget about sweating when you’ve got these on.

"I wore this top under the blazing sun on a hike at 16,000 feet and it didn't make me sweat," our tester said of the Patagonia design, which is also available in men's sizes. "I also wore it on a run and it did a great job of regulating my temperature and keeping me from overheating. On my run, I wore it as my only outer layer and it was raining very lightly, and I felt comfortable the whole time."

Price at time of publish: $139

The Details: XXS-XL | Wool, polyester

Travel + Leisure / Karen Chen

Ibex

Why We Love It: They keep you just as warm and comfy in freezing temperatures as they do in the mid-50s.

What to Consider: The neck hole is a bit tight.

If you plan to wear your thermals for a variety of activities, go for this set from Ibex. The versatile top and bottom are truly wear-everywhere thermals thanks to a warm yet breathable and sweat-wicking merino wool construction. One interesting feature unique to this Ibex Woolies set is a baste-stitch thumbhole on each sleeve. Choose to unstitch them for thumbhole use, or leave as is for more traditional use.

"During two separate wears — ice skating and leaf raking — the weather was quite different but the thermal underwear performed excellently!" our tester said. "The Midwest winter wind and freezing temperatures tried to ruin my skating adventure, but the layers kept me warm while also wicking away sweat. During leaf raking, the weather was in the 50s, and I was able to wear the thermal underwear under my jacket and be warm without overheating."

Price at time of publish: $135 for top, $135 for bottom

The Details: XS-XL | Merino wool

Travel + Leisure / Jeanne Geer

Smartwool

Why We Love It: They’re quite stylish and available in plenty of colors.

What to Consider: The top is long and boxy.

Our favorite thing about these base layers is that they don't look like base layers. That means you can feel free to go anywhere and do anything in them without looking like you just got off a ski lift or rolled out of bed. We also love that they’re soft, odor-resistant, thermoregulating, and designed with anti-chafing technology. Shoppers can also mix and match colors, as the top comes in 14 hues ranging from neutrals to pastels, and the figure-flattering bottoms come in eight colors.

"I would definitely recommend this set," our tester said. "It's warm, moisture-wicking, and also stylish enough that if for some reason you're caught only wearing your base layers, it doesn't look like thermal underwear. The top is especially versatile and can be worn on its own."

Price at time of publish: $110 for top, $110 for bottom

The Details: XS-XL | Merino wool

Travel + Leisure / Julia Sayers-Gokhale

Tani USA

Why We Love It: They aren't bulky at all, and they're stylish enough to wear alone.

What to Consider: The top runs short and the pants’ waistband is very thin, which may be uncomfortable for some shoppers.

Silk is surprisingly effective at regulating body temperature, which is why we love this thermal set. It's warm, breathable, and ultra-soft — not to mention, it features a sleek, flattering fit. Despite both the top and bottom's excellent insulation, they’re quite thin, so they’re ideal for layering under bulkier winter wear or wearing on their own. Get your hands on these in three shades and four sizes.

"I love the silky and thin feel," our tester said. "They don't feel bulky, and the material doesn't make me sweat like other thermal underwear I’ve worn. They feel very light and smooth on my skin; these would be easy to wear under my regular clothes."

The Details: S-XL | Modal

Travel + Leisure / Dwyer Frame

L.L. Bean Midweight Base Layer Top & Bottom: While our editors did like this crew neck and pants set, they felt it bunched around the ankles and had too loose of a fit for it to be practical. It also had to be aired out when it arrived, as it had a strange smell.

REI Co-op Midweight Base Layer Crew Top and Bottoms: Our testers found this high-value crew top and bottom set comfy for casual use, but it did not sufficiently keep them warm or wick away sweat on colder days or while partaking in snow sports.

Ridge Merino Women's Aspect Midweight Wool Base Layers: This thermal top and bottom did keep our editors warm, but they found them to be a bit too thick, tight, and scratchy. They also didn't have much stretch, so they failed to make our top picks.

Each tester was sent a pair of thermal underwear to assess. We first asked them to closely examine the sets’ quality and features and perform a stretch test by pulling them in every direction.They then wore the base layers for three separate wears: For the first wear, we tasked them with spending at least 30 minutes wearing the thermals in their home to judge comfort, fit, and warmth. For the last two wears, the testers spent at least an hour wearing the thermals outside while performing an activity like hiking, skiing, or running. To get a feel of the thermals’ durability levels, we also asked them to wash the garments at least once in the testing period and determine if doing so caused any shrinking, stretching, pilling, or other damage.

After all of the testing steps were completed, testers rated the thermals in six categories: comfort, fit, warmth, moisture-wicking, durability, and value. To receive a high score in comfort and fit, they had to be incredibly comfortable to wear for long periods of time during a range of activities and have a perfect level of stretch and compression to make you forget they’re even there. The best thermals for warmth and moisture-wicking exceeded expectations by keeping testers warm and dry throughout every test. Durability was based on the quality of materials, whether any signs of wear and tear were present after all uses and washes, and whether testers were confident they would last for a long time if frequently worn. Finally, we asked the testers to find out how much their thermals cost. High-priced items that scored well for value had incredibly high ratings in all other categories and testers could defend the price. For lower-priced items with a high value score, testers felt the quality was much higher than expected given the cost.

travel + leisure / Karen Chen

Material type is probably the most crucial aspect of base layers. Since they’re intended to be worn direct-to-skin and are often used for winter sports, moisture-wicking materials like merino wool, polyester, and elastane are usually your best bets. Wool in particular is also great for providing insulation while maintaining breathability. You’ll generally want to avoid cotton if you plan to wear your thermals for high-activity occasions, as it absorbs moisture and pulls heat away from the body, leaving you a soggy and shivering mess.

It may be tempting to choose thermals that are stylish, low in cost, or made by a name brand, but comfort should really be your first priority (especially considering your thermals will likely be covered by other garments). Sure, saving money or showing off your ‘fit is fun at first, but after a few hours of skiing, hiking, or camping, you’ll likely wish you opted for something that feels good on your body. Luckily, many of our picks above manage to be incredibly cozy without sacrificing style.

Thermal underwear or "long underwear" are base layers that can be worn alone or under heavier winter clothing like coats, ski pants, and jeans. They’re typically somewhat form-fitting to prevent bulkiness and overheating. The main function of thermal underwear is to add extra warmth during the colder months.

Most thermal underwear is form-fitting, but there are options that come in a more relaxed fit for those who prefer loose clothing. Thermals shouldn't be too loose, though, or else heat may escape and layering may be a challenge.

While it's technically up to you, most thermals are designed to be worn with underwear. If your base layers are on the looser side, it is especially important to wear underwear to prevent rashes, blisters, and discomfort.

For this article, T+L's outdoor enthusiasts personally tested dozens of thermals and gave feedback on their performance in comfort, warmth, fit, durability, moisture-wicking, and value. Editor Hillary Maglin consulted with T+L outdoor gear editor Lydia Price to determine which thermals are the best for every need and preference and completed additional research to help shoppers pick their perfect pair.

Love a great deal? Sign up for our T+L Recommends newsletter and we'll send you our favorite travel products each week.