The 10 Best Thermal Underwear of 2023

Our top pick is the Thermajane Long Johns Thermal Underwear, which is available on Amazon

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People / Brian Kopinski

Thermal underwear is a cold-weather essential that can be used for everything from snow sports to outdoor working conditions to everyday comfort and protection against the frigid winter air. Often worn under clothing — though some thermal underwear tops might be worn on their own depending on the material and type of coverage — this type of base layer insulates the body and is one of the most functional garments you can own.

Whether you’re hitting the slopes and need an extra layer of warmth for your ski outfit or live in colder climates and need everyday thermals to keep you nice and cozy, we’ve got you covered with the best thermal underwear styles, including long johns, leggings, onesies, long sleeve tops, and more.

Keep reading for PEOPLE's picks of the best thermal underwear.

Amazon

Someone looking for a thermal underwear set that is moisture-wicking and comes in lots of colors

Someone shopping for a more lightweight set that fits well under jeans and other everyday clothing items

For the best overall thermal underwear, we love the Thermajane Long Johns Thermal Underwear set from Amazon. This two-piece is designed to trap heat to the body with moisture-wicking technology, so you stay dry and comfortable in cold temperatures. Lined with fleece, the set can withstand frigid weather whether you’re wearing them at home or on the slopes. Additionally, they feature four-way stretch so they’re super comfortable, plus they’re thick enough to pass as leggings and a long-sleeve so you don't have to worry about transparent material.

Price at time of publish: $29.99

Material: 92% polyester, 8% spandex | Added Fabric Features: Moisture-wicking, heat retention, four-way stretch | Size Range: XXS-3XL

Amazon

Someone looking for a long-sleeve thermal with a zip-neck for hiking

Those shopping for pants or a onesie for hiking

If you’re on a budget and looking for thermal underwear with good value, you’ll find it in this set from Amazon. The DEVOPS Thermal Long Johns Underwear Leggings come in a two-pack in a variety of colors and are designed with spandex so they’re extra stretchy and form-fitting to the body for better heat retention. On top of that, they’re fleece-lined for an added layer of warmth.

Price at time of publish: $23.97

Material: 90% polyester, 10% spandex | Added Fabric Features: Fleece-lined, heat retention | Size Range: XS-XL

Patagonia

Someone looking for a long-sleeve thermal with a zip-up neck for hiking or other outdoor adventures

Someone who prefers to hike in a onesie or is looking for thermal pants only

The Patagonia Capilene Thermal Weight Zip-Neck is our top pick for a thermal long sleeve you can wear hiking. Designed for warmth and movement, this zip-neck top is constructed from recycled polyester and spandex with an open-grid pattern that form fits against the skin and provides lots of warmth. On top of that, the material is moisture-wicking, breathable, and features HeiQ pure odor-control to keep you feeling fresh while you summit.

Price at time of publish: $109

Material: 92% recycled polyester, 8% spandex | Added Fabric Features: Polartec Power Grid fabric, HeiQ pure odor control | Size Range: XXS-XL

Neiwai

Someone shopping for a base layer set that they can wear underneath garments

Those needing a set that is a little bit thicker and can be worn on its own

The Neiwai Classic Form-fitting Thermal Underwear Set is our top pick for the best set because it's the perfect option for thermal underwear worn as a base layer. With a thin, second-skin construction, the set is made from an acrylic, modal, and spandex blend that is designed for supreme heat retention and breathability. Available in three neutral tones, this is the perfect set to wear under ski and snowboard gear. One thing to note: This is final sale so won't be available to return or exchange.

Price at time of publish: $34 (orig. $68)

Material: 64% acrylic blend, 30% TENCEL modal, 6% spandex | Added Fabric Features: Heat retention, breathability | Size Range: S-L

UNIQLO

Someone shopping for an ultra-warm pair of thermal leggings at a super affordable price

Someone looking for a thermal top versus leggings

Uniqlo's line of Heattech gear is our winter weather go-to, thanks to its ability to insulate the body. If we had to choose one piece from the collection, it would be the leggings, which are lightweight yet ultra-cozy, as they are designed to provide supreme warmth and a second-skin fit. According to the brand, these 'Ultra Warm' leggings are 2.25 times warmer than the brand's original Heattech design. In addition to warmth retention, these leggings are breathable and moisture-wicking, so they can withstand outdoor activity while keeping you comfortable in the elements.

Price at time of publish: $19.90

Material: 38% polyester, 30% acrylic, 20% rayon, 12% spandex | Added Fabric Features: Moisture-wicking, breathable | Size Range: XS-2XL

Old Navy

Someone looking for an affordable, comfortable, and warm base layer to wear under their snow gear

Those instead shopping for a onesie or a set to wear under their snow gear

Add a layer of comfort to your snow sports gear with the Old Navy High-Waisted UltraBase Merino Wool Base Layer Tights. This pair of thermal underwear is constructed from a Tencel lyocell, merino wool, and spandex blend with four-way stretch and warm tech, keeping you ultra-warm, no matter what your cold-weather activity of choice is. On top of that, the leggings are super stretchy, so they comfortably move with you without restrictions. They’re also available in a fantastic size range, including tall and petite sizes.

Price at time of publish: $17.97 (orig. $39.99)

Material: 66% Tencel lyocell, 28% merino wool, 6% spandex | Added Fabric Features: Warm tech, moisture-wicking, four-way stretch | Size Range: XS-4X (tall, regular, petite)

Amazon

Someone looking for a cozy thermal onesie that is lightweight, breathable, and provides a layer of comfort

People shopping for a onesie with heat-tech or moisture-wicking properties infused in the fabric

The #followme Women's Thermal Henley Onesie Union Suit is a classic thermal onesie with its button-up design and lightweight yet ultra-cozy material. Constructed from a blend of cotton and polyester, the thermal is breathable and the ideal layering piece. However, it can also be worn on its own as pajamas for those looking for a pair of warm winter PJs. Available in a variety of colors, including some classic neutral as well as bright hues, theis thermal underwear also comes with a budget-friendly price tag.

Price at time of publish: $16.99

Material: 60% cotton, 40% polyester | Added Fabric Features: Breathable knit, button-up closure | Size Range: XS-XXL

Smartwool

Someone shopping for a pair of leggings constructed from wool

Those looking for a thinner pair of leggings that can be easily worn under pants or jeans

If you’re shopping for a pair of wool leggings, look no further than the Smartwool Women's Classic Thermal Merino Base Layer Bottom. These durable leggings are constructed from 100 percent merino wool with an interlock knit to help with thermoregulation. Merino wool is also naturally breathable and odor-resistant, so it's a fantastic option for active lifestyles. Designed with a slim fit, these leggings wrap around the body for an added layer of warmth and support, which is well-worth the higher price tag, in our opinion.

Price at time of publish: $110

Material: 100% merino wool | Added Fabric Features: Interlock knit, breathability, thermoregulation, odor resistance | Size Range: XS-XL

Parade

Anyone shopping for a thin layer long sleeve that provides lots of extra warmth

Someone shopping for a thicker fleece-lined top or one with a turtleneck

The best shirt to wear as a base layer is the Parade SuperSoft Warm Thermal Long Sleeve. Albeit lightweight, this thin top boasts tons of warmth as it form-fits to the body and regulates temperature even on the most frigid days. In addition to keeping you warm, the Tencel Lyocell top is also supremely breathable, so it is an excellent top to wear for outdoor snow sports or even just to go on a walk in the neighborhood in chilly weather.

Price at time of publish: $13 (orig. $26)

Material: Tencel Lyocell | Added Fabric Features: Temperature-regulating, breathable, antimicrobial | Size Range: XS-3X

Eddie Bauer

Someone shopping for a super-warm top for frigid temperatures with a built-in hood

Those instead looking for a pair of leggings or a set that can withstand intense frigid temperatures

A warm base layer is a must for extreme cold, and the Eddie Bauer Frigid Ridge Thermal Hooded Sweater is the best pick. This sweater is designed from a polyester, eco-vero, and merino wool blend with FreeHeat technology that keeps the body ultra-warm in the coldest of temperatures. On top of that, the overall design is constructed for maximum warmth and comfort, with a full-coverage hood and built-in balaclava to protect the face from frost.

Price at time of publish: $78.99 (orig. $99.99)

Material: 40% polyester, 35% eco vero, 25% merino wool | Added Fabric Features: FreeHeat technology | Size Range: S-XXL

When shopping for thermal underwear, the first thing to look at is the type of material it's constructed from. "Materials that provide moisture management and temperature regulation are ideal to keep you comfortable," says Denise Anderson, the head of global marketing at Smartwool. She recommends looking for thermal underwear made from merino wool, which is a natural fiber that is sustainable and ultra-warm. Some of our top picks, including the Smartwool Women's Classic Thermal Merino Base Layer Bottom and Old Navy High-Waisted UltraBase Merino Wool Base Layer Tights utilize merino wool's natural thermal heating capabilities to create undergarments that keep you cozy and comfortable. In addition to merino wool, you can also find thermal undergarments with advanced technology such as the UNIQLO Ultra Warm Heattech Leggings which are designed to keep you toasty in the most frigid of temperatures.

While fit is important to consider for anything you wear, it's especially important when it comes to thermal underwear. "Because you will most likely be layering over these pieces with mid-layers or outerwear, fit is an important consideration," Anderson confirms. "There are traditional cut-and-sew construction methods which may allow for more of a relaxed fit versus newer 3D knit technologies that are more form-fitting."

It's also necessary to consider the purpose or use since thermal underwear is a functional garment and needs to be able to serve its function well. With this in mind, Anderson says to consider what activities and in what climates you will be utilizing thermal underwear or base layers. "If you are looking for a layer for skiing, a 100 percent thermal weight base layer is ideal," says Anderson. "But if you are looking for a versatile layer for hiking in warm temperatures, a lightweight merino blend is perfect."

"It's an essential layer that provides comfort and temperature management in cold weather," says Jennifer Fisher, a senior designer at Eddie Bauer. "Thermal underwear and base layers are a very important and wise investment if you plan on enjoying the outdoors in a colder climate," she adds, noting that these layers need to feel soft on the skin, wick moisture away from the body, and help regulate body temperature.

If you’re on the hunt for the best thermal underwear, Fisher says that the fabric is what truly makes thermal underwear the best. "Because base layers are next to your skin, you want them to be soft and comfortable, but also perform really well by absorbing moisture and drying quickly, helping to maintain body temperature," she explains. Our best overall pick, the Thermajane Long Johns Thermal Underwear, is an excellent choice if you’re looking for a set in a variety of colors that is moisture-wicking and can withstand cold weather. If you’re looking for something durable enough to withstand winter sports (with a fantastic price tag), consider the Old Navy High-Waisted UltraBase Merino Wool Base Layer Tights, which are constructed from merino wool, a natural thermal material that is moisture-wicking and quick-drying and also has the ability to absorb odor caused by bacteria. "This means you can wear merino wool clothing for longer without having to worry about smelling," says Fisher.

"Thermals are a subset of base layers," says Nate Axvig, the founder of Aktiv, a Scandinavian outdoor clothing brand. The biggest difference between base layers and thermal underwear is that base layers are usually thinner, meant to be worn close to the skin, and are "used as a way to transport heat and moisture off of the skin." Thermals are also meant to be worn against the skin but Axvig says they tend to be a little thicker than base layers and have some added insulation to give warmth.

With that said, base layers and thermal underwear are used interchangeably to describe an added layer of clothing used for warmth. And while thermal often refers to thicker materials, base layers "can be made of any fabric and used from warm to cold conditions," says Anderson.

Thermal underwear and base layers might not be worth it for everyone; however, if you are an outdoor enthusiast or live in cold climates (or are visiting cold climates for that matter), they are a must-have. "The layer next to your skin is the most important in terms of keeping you comfortable during outdoor activities and can really make or break your experience," says Anderson.

Jessie Quinn is a contributing commerce writer for PEOPLE and has written for publications such as Byrdie, InStyle, The Spruce, NYLON, and more. When researching the best thermal underwear, she considered the material, fit, and performance, as well as the type of thermal underwear to find the best options for cold weather. She also connected with top thermal underwear experts Denise Anderson, Jennifer Fisher, and Nate Axvig to learn more about what to look for in high-quality and durable thermal underwear as well as gain insight into some of the most frequently asked questions about thermal underwear. As a result, she curated this list of the best thermal underwear pieces.