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We sweated it out on the slopes and while traveling to find the best thermals out there. christmas boxers
Rena Behar is a journalist and editor focusing on tech, travel, and gender. She has contributed to Travel + Leisure, TripSavvy, and more.
Sometimes, one pair of pants simply won’t cut it. Whether you’re hitting the ski slopes or taking a long walk around a new city, when it’s cold enough, you need a good thermal layer against your skin to keep your warmth locked in.
The best sets of thermal underwear will keep you cozy and dry (no coat sweat here), move with your body, and still look cute in the aprés-ski chalet. We tested a total of 24 sets of thermal underwear to find the best ones out there. After stretch tests, multiple wears, and plenty of outdoor activity, these are our favorites.
This set is comfortable, cute, and highly functional.
The pattern might not be to everyone’s preference.
Given that Kari Traa’s clothing is designed by its namesake, the Olympic champion skier, it should be no surprise that its base layers are super-soft, comfortable, and fitted just right, as well as actually stylish and fun to wear. They feel smooth and pleasant even for the wool-averse, to the extent that we wore them three days in a row on our first ski trip of the season. The set offers exactly the right layer of thickness, and we were equally as comfortable, thermoregulated, and dry on the slopes as we were in a heated city apartment or running errands. We found they manage to move with the body in a way that might surprise those who are new to wool layers.
The high zipped collar adds nice coverage without giving that choking feeling that can happen with high necklines, and the tapered waist and solid panels on the sides give it a flattering, fashionable look. And the excellent print doesn’t hurt either, giving the classic Alpine snowflake motif a modern edge. If you’re between sizes and want a little more wiggle room without giving up fit, you can size up; if you’d rather have a more compressive feel, size down. The fabric is also well-made, with sturdy-feeling seams and a smooth zipper. Ours even managed to survive an unexpected cat attack (apparently some cats love wool almost as much as we do). We didn’t expect “easy to brush cat hair off of” in our testing methodology, but it was a pleasant surprise.
These are super cozy and curve-friendly, and feel designed with active women in mind.
The sleeves and cuffs may be a little baggy.
We took these skiing in Sun Valley, Idaho, braving windy conditions and temperatures down to the teens, and stayed warm the whole time. The set feels soft and cozy, with zero itching, and the zipper is an excellent bonus to help regulate your temperature. They feel like very soft, thin sweatpants that perfectly hug your curves without digging in anywhere, moving with your body during activities, and can even be worn on their own if you wish.
We wore the top without an over-layer while relaxing at a summit lodge without ever feeling cold or soggy, even with all the sweat we worked up on the slopes. The design has held up against multiple wears and washes and as well as our second cat attack (perhaps we should enlist more feline testers). An additional bonus: unlike most of the competition, the brand uses numeric sizing, which makes it even easier to find your perfect fit.
These feel like your favorite sweats, plus they have high-quality materials and excellent temperature control.
The bottoms run a bit baggy and they may be too warm for some situations.
We started out testing this set with errands and long dog walks in New York, and quickly started wearing them nearly every day when working from home. They’re just as comfortable as sweatpants but look like thick leggings, so you can wear them out of the house just as easily. The top is equally lightweight and cozy, and the inside fleece is incredibly soft and warm. The top also fit perfectly, though we found that the bottom were a bit on the baggier side, which may cause them to slip a little during vigorous activity. They were also at some points almost a little too warm when paired with a parka on top while out for a walk, but we never felt damp underneath thanks to the excellent moisture-wicking. The quality materials and stitching live up to Arc’teryx’s high brand reputation, feeling thick and well-made; since we keep wearing them, we keep washing them, and there’s not a pill to be seen. We anticipate wearing them for many winters to come.
These were so comfortable that we kept them on for 16 straight hours.
We found they ran a little loose, so you may want to size down, and the fabric is on the thicker side.
This set was so comfortable, we ended up keeping these on for an entire day — for 16 straight hours including hiking. We simply loved wearing them. They’re super soft and warm, though the materials are on the thicker side of the base layer spectrum so felt a little bulky when we put fleece pants over them, but the top was super comfortable when worn solo under a jacket. We found they ran a little loose, so you may want to size down. But we stayed at the perfect temperature on hikes with temperatures in the 20s, and didn’t feel chilled at all when we took breaks. They also looked good as new after washing, and we plan to use them as our go-to base layer when ski season picks up. They’ve also got a good size range and number of colors to choose from, with 10 options in the top and eight in the bottom.
These thick, well-made layers do their job well and look great on their own.
They don’t layer as well under other tight clothing.
It’s always a bonus when your gear can do double duty in your everyday wardrobe. We’ve been longtime fans of Smartwool’s products, and their thermal underwear just reinforced that. Whether we were working, running errands, or attending an outdoor winter festival, we stayed warm but not sweaty. Both the top and bottom are on the thicker side, which means they can stand on their own as a shirt or leggings, though you may face some discomfort if you try to wear other tight clothes over them due to the slight bulk. They stayed in place well when we were active, though, and have impressive moisture-wicking abilities. The set feels high-quality and durable, like it should hold up for a long time to come on, and won’t feel out of place if you end up wearing it on its own. The extensive fun color options and even some prints, along with the availability of plus sizes, are the icing on the cake.
These have the perfect not-too-tight, not-too-loose fit and enough moisture-wicking and odor-absorbing ability to live through four straight sweaty ski days.
The material is very thin, so we have some minor concerns about potential durability issues.
In addition to our other tests, The Outdoor Research thermal underwear survived four straight eight-hour days of skiing without a wash in sight in the name of science. They were super comfortable straight out of the package; the fabric is thin for easy layering, as well as lightweight, soft, and breathable, and the fit is perfect. Both the top and bottom had just the right amount of stretch to let us move around freely, but were still tight enough to cling in place so they never felt bunched up or compressive.
Because they’re so light, our legs got a little cold on the mountain with just a shell over them, but our top half stayed warm thanks to multiple upper-body layers. We also never felt cold or smelly, no matter how much sweating we did, thanks to superb moisture-wicking. Because the material is so thin, we worry that they may get holes at some point, but they still seem as good as new after a year and multiple ski trips.
These are incredibly soft and not too clingy, so you can forget you have them on.
They may be a bit too loose for some, size down if you want a more formfitting set.
The Paka thermals are among the softest and most comfortable sets we’ve tested. The ribbed material doesn’t cling to skin the way leggings do, rather they loosely hug the body to provide warmth without discomfort. We’ve worn these alone with a parka on top for mild hikes and running errands, but the set fits well under snow pants, sweatpants, sweatshirts, and other outer layers.
We love that the thermal crew has a longer hem, so it comes down past the waist providing plenty of coverage if you want to wear these on their own and also preventing any cold spots around the middle. The thermal bottoms are cinched at the ankles as another way to prevent any drafts sneaking in.
We tested a total of 24 sets of thermal underwear to find the best pairs out there. First, we examined them immediately out of the package, performing a stretch test to investigate the feel of the fabric. Then, we put them on underneath our clothes for three different test wears: one lounging around at home for at least 30 minutes, and two separate outdoor activities, jaunts of at least one hour each. Afterward, we washed them according to the manufacturers’ instructions to see how they held up.
Each set was rated on comfort, fit, warmth, moisture-wicking ability, durability, and value. We also plan to keep testing them for another six months to see how they hold up over time.
Do you start to sweat at the slightest hint of cardio, or are you cold from the second you walk out your door until you get back inside again? Recognize your own temperature tendencies and plan accordingly. You’ll also need to consider what activities you’ll be doing in your thermal underwear; if you’re using them to tackle your commute or spring skiing, you can choose something a little lighter. If you’re spending a full day outdoors, however, you’ll want something heavier.
These are meant to keep you warm, after all. Look for fabrics that are both breathable and sweat-wicking, like wool or performance synthetics (ideally recycled), in addition to being warm.
If you’re hitting the slopes, you may very well work up a sweat on the downhill before you freeze again on your way back up the lift. Rather than letting that condensation suck the heat from your body, choose a moisture-wicking fabric that will pull it away from your skin and let you keep that precious warmth in (and minimize odor along the way). This way, you won’t feel soggy all day and will still be fresh for your post-ski festivities.
There can be few things more annoying than getting your sleeves squished up when you’re adding a layer. The solution: thumb holes. While these are my personal favorite features to look for in a base layer, you may also want to look for things like pockets, elastic around cuffs, and even a general attractive aesthetic for when it’s time to hit the apres-ski. The quarter-zip neck on our favorite pair, for example, both lets you adjust for ventilation and gives the top that extra touch so you can wear it on its own.
Once you’ve chosen your fabric type, there are degrees of intensity. For merino wool, there’s a convenient grams per square meter weighting system: the higher the number, the thicker the wool, and so the warmer the item. Light wool has a GSM of 150-190, medium is 200-300, and more than 300 is the heaviest. Synthetics aren’t quite as straightforward, so you’ll have to rely on checking the feature lists and hand feel, though some brands, like Polartec, do have different styles of fleece that offer different insulation levels. It usually helps to check a brand’s website to assess its different product levels.
Ideally neither — the best thermal underwear has a snug but not compressive fit. If you must choose (like if you’re between sizes), you probably want to err on the tighter side, without going so far as to cut off your circulation or make the layers dig into you when you add more clothes over them. A sufficiently snug fit, however, will keep your base layer from annoyingly wrinkling up or moving around underneath your other clothes.
That depends on a few things. We’re assuming you’re wearing your regular underwear as well, so you don’t necessarily need to wash it after every wear. You’re safe to wait until it gets dirty or, more likely, a little sweaty or stinky. And with the help of odor-absorbing and antibacterial materials, you’re likely to get at least a few wears in before it’s wash day.
Rena Behar is a long-time writer, traveler, snowboarder, and constantly cold person. She has worn many sets of thermals in her time and values a set that remains in place for the full day. For this article, she worked with Travel + Leisure editors and combed through real-world testing insights to determine the best sets for all users.
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