13 Thermal Underwear Sets You Won’t Want To Take Off All Winter

It’s never too early to stock up on your cold weather essentials. In addition to a cozy pair of flannel pajamas and a down (or down alternative) jacket, you won’t regret adding a good pair of thermal underwear to your winter shopping list. When the air gets cold and snow starts to fall, the right base layers can keep you comfortable in any conditions.

Best thermal underwear sets at a glance

• Best merino wool (women’s): Smartwool Women’s Merino 250 Base Layer Bottom, $110
• Best odor control: Ibex Women’s Woolies Tech Base Layer, $115
• Best budget (women’s): Thermajane Women’s Ultra Soft Thermal Underwear Set, $26
• Best lightweight (women’s): Patagonia Women’s Capilene Thermal Weight Bottoms, $90
• Best boxer shorts: Stoic Women’s Merino Boy Boxer, $37
• Best seamless: Sweaty Betty Betty Ski Merino Base Layer Leggings, $148
• Best ultra thin: Terramar Women’s Thermasilk Pointelle Pant, $41
• Best merino wool (men’s): Icebreaker Men’s Merino 175 Everyday Thermal Leggings, $85
• Best for super warmth: Kora Men’s Yushu Bottoms, $130
• Best for outdoor activities: Under Armour Men’s ColdGear® Base 3.0 Leggings, $70
• Best budget (men’s): At The Buzzer Men’s Thermal Underwear Set, $17
• Best lightweight (men’s): Tani SilkCut Thermal Underwear Set For Men, $145
• Best fleece-lined: Thermajohn Men’s Ultra Soft Long John Set, $27

Before you buy, know that not all thermal underwear sets are created equally. While you can find affordable options at most major retailers, the right materials and design can make all difference. Your base layers should retain body heat without leaving you itchy, scratchy, or sweaty. Look for thermals that use temperature-regulating fabrics, like wool and spandex, to stay warm without overdoing it.

Keep an eye on design, too. Most thermal underwear serves as a base layer underneath other clothing—you want tops and bottoms with clean, tight silhouettes, but aren’t so restrictive they becomes uncomfortable. Keep scrolling to shop 13 of the best thermal underwear pieces from brands like SmartWool,Ibex, and more.

13 of the best thermal underwear to layer up in this winter

Best thermal underwear for women

Best merino wool (women's): Smartwool Women's Merino 250 Base Layer Bottom — $110.00

Smartwool is a smart investment. Like all Smartwool products, these leggings (or thermal undies) are crafted from Merino wool, which is known being moisture-wicking, antimicrobial, and super comfortable. Available in black, navy, and various heather options.

What reviews say: “The instant you pull these base layers out of the package you know you’re dealing with a quality product. I work for a gear retailer so I’ve had the chance to handle many base layers and these are by far my favorite.” — Smartwool customer

Material: Merino wool

Sizes: XS-XL

Pros

• Thermo-regulating
• Flatlock seam construction to minimize chafing
• Machine-washable

Cons

• Some reviewers say they stretch out with wear

Best odor control: Ibex Women's Woolies Tech Base Layer — $115.00

Similarly, Ibex also makes premium products all made from high-quality Merino wool. These best-selling thermal undies are warm without ever being stuffy or sweaty. Throw them on under snow gear, jeans, leggings—whatever you need to layer up.

What reviews say: “Great for staying warm inside during winter and a great base layer. These natural fibers don’t retain odor like the synthetic fibers. Always a great addition to a wardrobe.” — Taunya M., Ibex customer

Material: Wool, nylon, elastane

Sizes: XS-XL

Pros

• Moisture-wicking
• Odor control
• Flatlock seam construction to minimize chafing
• Machine-washable

Cons

• Some reviewers say they are not thick

Best budget (women's): Thermajane Women's Ultra Soft Thermal Underwear Set — $26.00

For just $30, snag this best-selling thermal underwear set off Amazon and stay snuggly all winter long. Instead of wool, these are made from a lightweight poly-spandex blend that’s still warm enough to keep body heat where it belongs. They’re also fleece-lined for added warmth.

What reviews say: “Bought a set of these thermals in each color for my trip to Alaska over the Thanksgiving holiday…  At -14 degrees they kept me warm and they are super soft and comfortable.” — Amazon customer

Material: Polyester, spandex

Sizes: XXS-3XL

Pros

• Affordable
• Four-way stretch
• Comes as a set
• Moisture-wicking
• Machine-washable

Cons

• Some reviewers say the fabric pills

Best lightweight (women's): Patagonia Women's Capilene Thermal Weight Bottoms — $90.00

Breathable but still tight-knit, these thermal bottoms from Patagonia are made with spandex for better movement and flexibility. Between the flat seams, stretchy waistband, and supple fabric, they’re comfortable and get the job done when the temperature falls.

What reviews say: “I have just purchased my third pair. They are light in weight but provide great warmth in the cold. I spend a lot of time hiking, snowshoeing, and cross country skiing.” — Irene, Patagonia customer

Material: Polartec PowerGrid fabric, spandex

Sizes: XS-XXL

Pros

• Breathable and moisture-wicking
• Odor control
• Flat waistband
• Made with recycled materials

Cons

• Some reviewers say the fabric is sheer

Best boxer shorts: Stoic Women's Merino Boy Boxer — $37.00

When you want warmth without the bulk, layer on these Merino wool boxers from Stoic. The stretchy, flat seaming won’t ever dig or chafe. Great for cold weather workouts and gym sessions when shorts alone won’t cut it. Available in black and grey.

What reviews say: “These are perfect wicking underwear for hiking and camping. My second time purchasing them.” — Amazon customer

Material: Merino wool, elastane

Sizes: XS-L

Pros

• Moisture-wicking
• Odor control
• Stretch construction
• Flatlock seam construction to minimize chafing

Cons

• Some reviewers say they have a very high waist

Best seamless: Sweaty Betty Betty Ski Merino Base Layer Leggings — $148.00

Arguably the prettiest thermal underwear on this list, these thermal leggings from Sweat Betty are just as functional as they are fashionable. They’re seamless and sweat-proof, made from dreamy Merino wool that’ll keep you cozy on the slopes and beyond. Available in black.

What reviews say: “I love the SB merino base layers as they are so warm and comfortable. If I am not on the slopes I pop them on under my jeans – such a perfect extra layer in these cooler months.” — Sweaty Betty customer

Material: Merino wool blend

Sizes: XS-XL

Pros

• Available in 7/8 and full length
• Seamless
• Temperature-regulating
• Sweat-wicking

Cons

• Expensive

Best ultra thin: Terramar Women's Thermasilk Pointelle Pant — $41.00

These thermal bottoms are made from 100 percent filament silk that fit seamlessly underneath any kind of outerwear. They’re also thermoregulating, so you’ll never overheat, and UPF 50 for added protection. Available in black, grey, white, and pink.

What reviews say: “I use this and a matching top to sleep in when I am out backpacking in the back country. Warm or cool, these are perfect for staying comfortable at night.” — Amazon customer

Material: Filament silk

Sizes: XS-XL

Pros

• UPF 50+
• Moisture-wicking
• Machine-washable

Cons

• Material is thin

Best thermal underwear for men

Best merino wool (men's): Icebreaker Men's Merino 175 Everyday Thermal Leggings — $85.00

Icebreaker is another premium purveyor of all-things thermal. Its line of Merino wool base layers are versatile and reliable, guaranteed to do their job no matter where you roam.

What reviews say: “This was everything I was expecting and I am so glad I bought two pairs! Perfect winter gear for living in the cold city or hiking in the high country.” — Icebreaker customer

Material: Merino wool

Sizes: S-XXL

Pros

• Thermo-regulating
• Lighweight
• Slim fit
• Machine-washable

Cons

• May not be as stretchy

Best for super warmth: Kora Men's Yushu Bottoms — $130.00

Kora products are made from Merino and yak wool, making them ridiculously warm in even the coldest climates. These full-length pants fit smoothly under bibs, snow pants, and more, making them perfect for just about any winter activity.

What reviews say: “This is the second item we have tested from Kora and we are impressed. If you appreciate natural materials and want a very high performing base layer, then look into yak wool!” — Engearment review

Material: Yak and merino wool

Sizes: S-XXL

Pros

• Super warm
• Breathable
• High-wear crotch panel
• Flat seams

Cons

• Expensive

Best for outdoor activities: Under Armour Men's ColdGear® Base 3.0 Leggings — $70.00

This all-season base layer is great for everyday wear, in and out of the gym. The brushed grid interior traps air, maintaining an even (but warm) body temperature as you work up a sweat. Excellent for adding heat but never bulk.

What reviews say: “Since my passion always takes me outdoors, winter time is my favorite time of the year. The cold gear base layer has never disappointed me. It is fantastic in the cold weather whether I’m skiing, snowshoeing or even snowmobiling.” — Under Armour customer

Material: Merino wool

Sizes: S-3XL

Pros

• Sweat-wicking
• Four-way stretch
• Scent control technology
• Traps heat in

Cons

• Some reviewers say the waistband is loose

Best budget (men's): At The Buzzer Men's Thermal Underwear Set — $17.00

This top-selling thermal underwear set has more than 5,000 reviews on Amazon and is less than $20. It’s made of a cotton-poly blend that’s snug but never stiff or uncomfortable. A great, budget-friendly option for quality thermals.

What reviews say: “Love these thermals. Great quality for the price and I love how vibrant the red is even after several washes. Keeps me perfectly warm in a NY winter without being too uncomfortably heavy when transitioning from outside to indoors.” — Amazon customer

Material: Cotton, polyester

Sizes: S-3XL

Pros

• Traditional thermals
• Comes as a set
• Comfortable fit
• Machine-washable

Cons

• Does not have a snug fit

Best lightweight (men's): Tani SilkCut Thermal Underwear Set For Men — $145.00

This luxurious thermal set is made from all natural materials that are biodegradable, making them the eco-friendliest option on this list. Both the top and bottoms are soft and stretchy, made of a thin-yet-durable fabric designed to keep you cozy while you wear.

What reviews say: “Outstanding in feel, quality, and warmth! Hate having to take them off!” — Kip H.,  Tani customer

Material: Micro Modal Air, elastane

Sizes: XS-XXL

Pros

• Fabric is lightweight but durable
• Comes as a set
• Breathable and moisture-wicking
• Made from natural materials
• Machine-washable

Cons

• Expensive

Best fleece-lined: Thermajohn Men's Ultra Soft Long John Set — $27.00

The number one men’s best-selling thermals affordable enough to snag a set in every color. The poly-spandex blend wicks moisture and sweat, keeping you dry and cool when you get moving.

What reviews say: “These long johns are thin enough, very comfy, and close fitting around the wrists, ankles and waist. Wearing them under daily clothes during winter is very practical.” — Amazon customer

Material: Polyester, spandex

Sizes: XS-X4L

Pros

• Moisture-wicking
• Fleece-lined
• Four-way stretch
• Built-in fly

Cons

• Some reviewers say they run small

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