The Best Thermal Underwear of 2024, Tested and Reviewed

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Keep comfortable and warm no matter how cold the weather gets thanks to thermal underwear.

In This Article

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 (or long 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, we tested dozens of sets and selected our favorites for various needs and situations.

In addition to the top-tier athletic performance, it's sleek, figure-flattering, and comes in fun wintry prints.

It's 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.

The Details: XS to XXL | Merino wool

This comes in 10 different sizes, ranging from size 0 to 18, for plenty of fit options.

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, and they 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.

The Details: 0 to 18 | Merino wool

Travel + Leisure / Lydia Price

The wool and synthetic blend is both breathable and lightweight underneath outer layers.

Our legs were a bit cold while skiing with shell bibs in below-freezing temperatures.

Outdoor Research's Women's Alpine Onset Merino 150 Crew top and bottoms are our favorite pair of breathable and lightweight base layers. The material is on the thinner side but the set still proved to be warm underneath ski gear and comfortable to wear while out about running errands. When we got sweaty while skiing, the top dried quickly without losing warmth (shoutout to the merino wool fibers) and the light material made it easy to layer a jacket or two over the top. Merino wool is also naturally odor-resistant, so we were able to wear the set three days in a row without any funky smells. Our legs got a little chilly while skiing with shell bibs on, so if you're planning to use these for skiing, you may want to layer the pants as well. Men's size options and styles are also available.

The Details: XS to 4XL | Merino wool, recycled polyester, elastane

This baselayer top doesn't feel too heavy or bulky but will keep you warm on mild winter days.

It didn't wick away sweat as well as we would have liked.

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 pick 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, but these are not quite as warm as other options, so we think these would be best for spring weather.

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

They’re extremely soft and cozy.

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. 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 will involve sweat or other moisture. But if you want a budget-friendly way to stay cozy day-to-day, these are perfect.

The Details: XS to XXL | Polyester, spandex

The material is thick and warm without feeling constricting.

The base layers are designed for temperatures below 50 degrees Fahrenheit.

We're big fans of Smartwool's Intraknit crew neck top and bottoms for extra chilly days on the mountain skiing. Made with a thick blend of merino wool and synthetic fibers, this set of thermal underwear kept us perfectly warm on the slopes of Vermont during a frigid winter day. With the perfect balance of compression and stretchiness, the top and bottoms are both warm and breathable, and the wool fibers naturally wick away moisture and odor, which is ideal for rigorous activities. These are a little thicker than your average base layer, but they don't feel bulky when layered underneath clothing. One thing to consider is that the thermal underwear is designed for 50-degree weather or colder, so you may want to wear this set without any other layers if you're doing some spring skiing.

The Details: XS to XL | Merino wool, polyester, elastane

It's available in regular, tall, and big sizes.

It's 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.

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

This expertly wicks away sweat, even during high-intensity activities like running and hiking.

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.

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

It's soft, warm, and made with several barely-noticeable pockets.

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. 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.

The Details: XXS to XXL | Nylon, polyester, elastane

It's quite stylish and available in plenty of colors.

The top is long and boxy.

Our favorite thing about this base layer is it doesn't look like a base layer. That means you can feel free to go anywhere and do anything without looking like you just got off a ski lift or rolled out of bed. We also love that it's 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.

The Details: XS to 4XL | Merino wool

L.L.Bean Midweight Base Layer Top & Bottom: While we did like this crew neck and pants set, we 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: We found this high-value crew top and bottom set comfy for casual use, but it did not sufficiently keep us 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 us warm, but we 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.

We tested 24 sets of thermal underwear while skiing, snowboarding, running outside, and conducting everyday activities. We first closely examined each set’s quality and features and performed a stretch test by pulling them in every direction. We then wore the base layers for at least three separate wears. For the first wear, we spent at least 30 minutes wearing the thermals at home to judge comfort, fit, and warmth. For the last two wears, we 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 washed the garments at least once in the testing period and determined if doing so caused any shrinking, stretching, pilling, or other damage.

During testing, we judged the thermals based on comfort, fit, warmth, moisture-wicking, durability, and value. To receive good marks, 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 that made us forget they were even there. The best thermals for warmth and moisture-wicking exceeded expectations by keeping us 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 we were confident they would last for a long time if frequently worn. Finally, we evaluated the thermals' cost, looking to see if an item's price felt fair. This test continued over a period of two months.

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, making it an excellent option when choosing layers for travel. 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.

Travel + Leisure / Lydia Price

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.

Travel + Leisure / Anna Popp

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.

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