The Best Thermal Underwear for Men and Women, Tested and Reviewed

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TripSavvy / Marcus Millan

TripSavvy's Picks

Our testers loved the performance and style of Patagonia’s Capilene Air Crew and Bottoms saying they felt comfortable transitioning from cardio activities to cafes and restaurants. Meanwhile, Kari Traa’s Merino wool blend impressed our testers, particularly with winter activities like skiing.

A good layering system is key to enjoyable winter recreation. And that starts with a solid base layer. We spent weeks hiking, running, skiing, and lounging in 22 pairs of thermal underwear to find the best pair for you. Each set of thermal underwear earned scores on a five-point scale for comfort, fit, warmth, durability, moisture-wicking, and overall value. We then averaged those scores to create overall scores for each thermal underwear set.

We’ve spent hundreds of hours in these thermal underwear base-layers hiking, walking dogs, snowboarding, skiing, running, lounging, and going to outdoor music festivals. These are the thermal underwear sets we love the most.

Best Overall

Patagonia Women's Capilene Air Crew

4.5
Patagonia Women's Capilene Air Crew

Patagonia

What We Like
  • Excellent at wicking moisture and drying

  • Soft and stretchy, so good for outdoor activities

  • Stylish enough to wair from trail to town

  • Good stink-resistance

What We Don't Like
  • Patagonia improved the durability, but we’re still a bit concerned about it

Don’t let Patagonia’s 3-D Knit fool you. As our tester noted, Patagonia’s Capilene Air comes off as “not smooth or particularly soft,” yet the material moves and stretches with you easily while being active. That’s thanks to the brand’s merino wool and recycled polyester blend that employs a proprietary “Airblasting Technology” that improves dry-time, durability, and moisture-wicking.

Our tester wore this base layer on a hike in Peru and complimented the shirt’s ability to regulate body temperature at 16,000 feet of elevation. She also took it on multiple runs in New York, where it also wicked moisture and dried quickly. “These surprised me with how comfortable and lightweight they felt while still being great at regulating temperature and keeping me feeling dry even after cardio activity,” our tester concluded. “I do like this top because it could easily transition from the trail to lunch or from the ski slopes to apres. Because of the knit texture, it almost looks like a sweater, so you could definitely wear this out and about, and it wouldn't necessarily look like thermal underwear.”

Style: Midweight | Materials: 51 percent responsibly sourced merino wool, 49 percent recycled polyester | Sustainability: Uses responsibly-sourced merino wool and recycled materials

Best Overall, Women’s-Specific

Kari Traa Rose Set

kari-traa-rose-set

Amazon

What We Like
  • Excellent at temperature regulation

  • Soft with good stretch

  • The half-zip design adds some versatility

What We Don't Like
  • Nothing yet

Like Patagonia’s Capilene line, Kari Traa’s Rose thermal underwear set is a classic. Constructed with 100 percent merino wool, these midweight base layers also feature four-way stretch, which our tester found moved well with her body. Our tester, who has skin that’s very sensitive to traditional wool, found the merino wool “very pleasant to wear.” In particular, she appreciated the breathability with insulating warmth that makes the material so popular.

Also, like the Capilenes, the Rose set has a slim, athletic cut. Our tester tried two sizes and appreciated the difference in each. “The bigger size has a bit of wiggle room while still being fitted, and the smaller provides a slight compression and is perfect for layering,” she reported. We also appreciated the half-zip design for the top layer as it provides a bit more versatility and a way to release heat while participating in higher-output activities."

Style: Midweight | Materials: 100 percent merino wool | Sustainability: Not listed

Best Overall, Runner-Up

ODLO Women's Performance Wool Warm Long Sleeve Base Layer

4.8
ODLO The women's Performance Wool Warm long sleeve base layer

ODLO

What We Like
  • Good stretch without feeling constricting

  • The midweight level is ideal for most winter sports, with other layers

  • Stench-resistant

What We Don't Like
  • Could be better at moisture regulation

ODLO’s Performance Wool Base-Layer set has an interesting blend of mostly merino wool with a touch of polyester, polyamide, and elastane. The result is a set of thermal underwear ideal for most winter sports and activities. “These layers fit like a second skin,” our tester said. “I have other wool base layers from Ibex, Smartwool, and Icebreaker; these are as good, if not better, with nice stretch without feeling constricting.”

Our tester took these ice skating, wearing jeans over the bottoms and a shell jacket over the top. And while the jeans became heavy and clammy while working up a sweat skating, our tester reported feeling comfortable and mostly dry when she finished. Bonus: Even with the half blend of merino wool, our tester said the fabric didn’t retain odors despite multiple wearings.

Style: Midweight | Materials: 52 percent merino wool, 29 percent polyester, 13 percent polyamide, 6 percent elastane | Sustainability: Not listed

Best Budget, Women’s

PISIQI Thermal Underwear Women Ultra-Soft Long Johns Set Top & Bottom

4.7
Long Johns Set Base Layer

Amazon

What We Like
  • Good temperature regulation

  • Also good softness and comfort

What We Don't Like
  • Might not be the best for high-output activities

If some of the prices of other thermal underwear on this list seem ridiculous, we don’t blame you. Or if you’re only wearing base layers a few times a year, you might consider a budget option. We love the thermal underwear set from PISIQI. Like other higher-priced base layers on this list, the PISIQIs have four-way stretch and breathable fabric that our tester found to be just the right layer while taking walks with temperatures in the mid-30s.

Style: Midweight | Materials: Polyester | Sustainability: Not listed

Best Budget, Men’s

Carhartt Force Midweight Mirco-grid Base Layer Top

4.6
Carhartt Force Midweight Mirco-grid Base Layer Top and Bottom

Carhartt

What We Like
  • Excellent warmth

  • Good moisture regulation and durability

  • The shirt has a zippered pocket

  • Large range in sizes, so would also work well for bigger and plus-sizes

What We Don't Like
  • Fabric was itchy at first but got better after washing a few times

  • Size up one size

True to Carhartt’s reputation, the Force Micro Grid Base-Layer Set was incredibly warm and durable while our Northern California-based tester took them out for some early-season Snowboarding at Lake Tahoe. The Force set features a 100 percent polyester construction with a grid system that reminded our tester of Polartec’s grid fleece material. Our tester reported snowboarding when temps were around 30 degrees using just a shell.

We did have two issues. First, the material was itchy until multiple washes when it began to get more comfortable. Second, our tester says to size up as they were already a bit small and shrunk more in the wash. But one thing we like about this set of thermals is they come in a wide range of sizes, including plus sizes, so it should be easy to size up a bit.

Style: Midweight | Materials: Polyester | Sustainability: Not listed

Best Midweight

Smartwool Women's Classic Thermal Merino Base Layer Crew

4.6
Smartwool Women's Classic Thermal Merino Base Layer Crew

Smartwool

What We Like
  • Excellent at moisture-wicking

  • Good durability

  • Ideal choice for all-around winter activities

What We Don't Like
  • Previous versions have had durability issues, but so far, these seem to hold up

Smartwool was one of the original brands to employ merino wool in its outdoor activity socks and base layers. Originally from Steamboat Springs, Colorado, the brand has its roots in creating products for outdoor winter activities in sunny, cold conditions. These classic midweight layers excel at just that, providing excellent moisture-wicking and warmth for most winter activities.

Our tester took these on multiple walks and errand trips in 30-degree weather and to an outdoor festival when temps dipped into the 20s. She found them ideal for both situations, and while cold at the beginning of the festival, she felt they warmed up quickly with brisk walking. If you’re looking for a pair of thermal underwear to layer underneath tight clothing or during high-output activities like running, this may not be the best base layer. But for hiking, skiing, or wearing to walk the dog, they’ll be excellent.

Style: Midweight | Materials: 100 percent merino wool | Sustainability: Not listed

Best for Skiing and Snowboarding

Ibex Women's Woolies 2 Crew

4.7
Ibex Woolies 2 Crew

Ibex

What We Like
  • Perfect material thickness for layering or wearing alone

  • Fit very well around the body

  • Excellent warmth and moisture-wicking

What We Don't Like
  • Our tester reported some itchiness

Ibex might be a lesser-known brand than Smartwool, but the brands are quite similar in thermal underwear. The Woolies 2 line from Ibex features 100 percent merino wool and a very minimalistic yet effective design and construction. That merino build impressed our tester with how warm and regulating this base layer was in multiple conditions.

While raking leaves with temps in the 50s, our tester reported wearing the Woolies 2 underneath one jacket and staying warm without overheating. Our tester reported that the thermal underwear still performed well when conditions worsened during an ice skating outing. “The Midwest winter wind and freezing temperatures tried to ruin my outdoor ice skating adventure, but the layers kept me warm and protected against the cold while also wicking away any sweat from ice skating,” our tester reported.

We were also impressed by the fit of the Woolies 2. “I loved the fit of the thermal underwear all around the body. From the top to the leggings, the material hugged my body versus restricting it,” our tester said.

Style: Midweight | Materials: 100 percent merino wool | Sustainability: Not listed

Best Multi-Use

Minus33 Franconia and Ossipee

minus33-franconia-and-ossipee

Minus33

What We Like
  • Very warm

  • Excellent at stink reduction

  • Great moisture wicking and temperature regulation like other merino wool products

  • UPF protection

What We Don't Like
  • Can be a bit bulky under tighter layering

Minus33 is another brand (like Ibex) that is lesser known, but makes very quality merino wool products that we love for most winter, late fall, and early spring activities. These thermal underwear pieces include 100 percent merino wool with an interlock knit, which helps improve durability, moisture-wicking, and comfort—something our tester was thoroughly impressed with. We put this thermal underwear as our best for multi-use because of its UPF protection, making it ideal for layering and wearing as a stand-alone layer in warmer temperatures.

Our tester took this thermal underwear set hiking when temperatures were in the high 20s and wore nothing over the pants and just a light softshell over the top. She found them very comfortable and ended up wearing them all day. The moisture-wicking helped keep her from getting chilled once she stopped hiking, and she was impressed with wearing the base layers multiple times between washes without stink.

Style: Midweight | Materials: 100 percent merino wool | Sustainability: Not listed

Best Lightweight

Arc'teryx Women's Rho LT Zip Neck Base Layer

4.7
Arc'teryx Rho Women's Rho LT Zip Neck Base Layer

Arc'teryx

What We Like
  • Very cozy and soft on the inside

  • Quarter-zip top is nice and adds versatility

  • Excellent quality and all-around performance

What We Don't Like
  • Pants run a bit big, so consider sizing down if looking for true compression or tight-fitting bottoms

Arc’teryx’s RHO LT (lightweight) top works well for lower-output activities in cold and cooler temperatures. Our tester found them the perfect base layer for walking her dog in New York weather when temperatures were in the upper 30s. The proprietary “Torrent” fabric impressed our tester with how cozy and comfortable it was, yet also excellent at temperature and moisture regulation. The “Polygiene” odor control also helps reduce stink and minimize washing.

Still, these are not the most breathable base layers we tested, which is one reason why we recommend them for lower-output activities, like light hikes, dog walks, and trips to brunch. That said, even with the higher cost, our tester still highly recommends them for lounging on winter days and for light activities.

Style: Midweight | Materials: Proprietary Torrent fabric with Polygiene odor control | Sustainability: Not listed

Best Synthetic

Under Armour Women's UA Base 3.0 Crew

4.5
Under Armour Women's UA Base 3.0 Crew

Under Armour

What We Like
  • Cut for activity and have a slim fit

  • Warm and breathable

  • Good for higher-output activities in the cold

What We Don't Like
  • Could use more stretch

Our tester took Under Armour’s UA 3.0 Base-Layers on multiple hikes and runs in 30-degree temperatures, some up to three hours long. The upshot? These base layers excel at providing warmth and breathability but do not stretch as well as others, despite using a four-way stretch. Not surprisingly, considering the brand, our tester found this thermal underwear performed best while doing high-output activities in the cold.

“When I wore them on a hike, I felt dry the whole time, even after 1.5 hours of hiking uphill,” our tester said. “This fabric feels like it has a very tight, high-quality weave. I would trust these in very cold conditions, including those where I sweat a lot—like cross-country skiing—to keep me dry.”

Style: Midweight | Materials: 81 percent polyester, 19 percent Elastarell | Sustainability: Not listed

Other Thermal Underwear We Tested

In total, we tested 22 pairs of thermal underwear. Here are the other sets we tested not mentioned above: Thermajane Long Johns Thermal Underwear, Uniqlo Heattech Ultra Warm Long Underwear, TSLA Thermal Underwear set, Tommy John SleekHeat Long Johns, REI Co-op Midweight Base Layer, Helly Hansen Lifa Base Layer, L.L.Bean Midweight Base Layer, Ridge Merino Aspect Midweight Base Layer, Icebreaker BodyfitZone Thermal Underwear, L.L.Bean Silk Pointelle, Terramar Thermasilk, and Tani Silkcut.

How We Tested

We first researched top-performing thermal underwear based on customer reviews on sites like Amazon, REI, and Backcountry, looking to see other thermal underwear featured in other prominent publications, and from the expertise of our own editors and writers. We narrowed the list to the 22 above.

Testers rated thermal underwear on comfort, fit, warmth, moisture-wicking, durability, and value while also considering temperature regulation. Each tester rated the thermal underwear on a five-point scale for each category. Then we averaged those ratings to create the best overall thermal underwear.

Testers took the thermal underwear skiing, snowboarding, hiking, running, walking, errand-running, to outdoor festivals, and other activities. Our testers are based across the country, from New York to the Midwest to California, and also took the thermal underwear on trips with them.

What to Look For in Thermal Underwear

Material

Material is probably the most important thing to consider when picking a pair of thermal underwear. Generally, materials will be merino wool, a synthetic (like polyester or other proprietary materials), and silk. For most activities, we prefer merino wool or a synthetic blend. Merino wool has rapidly become the go-to pick for most outdoor enthusiasts because of its natural moisture-wicking, temperature-regulating, and stink-reduction properties. We love the material, particularly its stink-blocking abilities, which means you don’t have to wash the item as much, increasing the clothing item’s life.

Merino wool isn’t your grandparent’s wool that you might be thinking of. It’s very soft and comfortable. That said, our testers that were extra sensitive to itchy or irritating wool did report some annoyance with a couple of the merino wool thermal underwear sets. If you tend to get irritated by wool, opt for a synthetic, like the Under Armour option above.

Activity

Also consider your activity or activities for which you’ll be using the thermal underwear. You'll want a synthetic or lighter-weight merino wool blend for higher-output activities like running, cross-country skiing, or backcountry skiing. But a midweight merino wool base layer is probably best for resort skiing, hiking, lounging, apres, or dog walks.

Fit

Thermal underwear should fit like underwear, meaning close to your skin. It doesn’t have to fit like compression wear, but it should be close to your skin to prevent chafing and help with moisture wicking and temperature regulation. Also, consider how you’ll be layering. Do you plan on putting tighter layers on over the thermal underwear? You might opt for something very tight-fitting and lighter-weight. Are you going to layer bulkier items like ski clothing over it? You can probably get away with bulkier or mid- to heavier-weighted thermal underwear.

Weight

Generally, thermal underwear will come in lightweight, midweight, and heavyweight cuts. This essentially means the thickness of the material. As you might’ve noticed on our list or from your own research, the most common weight is midweight. That’s because it’s the best overall weight for a larger temperature range and most activities. For most people, a midweight base layer is best.

But if you’re looking for thermal underwear for highly-specific activities like running or cross-country skiing, or if your climate isn’t super cold, consider a lightweight layer. Likewise, if the purpose of your thermal underwear is to stand or sit outside for long periods or you live in an exceptionally cold climate, consider a heavier-weight pair.

Frequently Asked Questions
  • How do I care for and clean my thermal underwear?

    Always follow the manufacturer's recommendations. That should be on a tag on the inside of your thermal underwear. If not, consult the manufacturer’s website for the specific item you own. Generally, we recommend washing on cold and hang-drying. We also recommend hang-drying your long underwear immediately after removing it after activities.

  • Is all thermal underwear odor-resistant?

    No. But most are to varying degrees. Merino wool is naturally odor-resistant, and we recommend opting for merino wool thermal underwear if odor resistance is important to you (it is to us). That said, even with synthetic materials, most brands will use some form of a stink-blocking coating or build stink-blocking qualities into the synthetic fabric.

  • Is there a difference between thermal underwear and a base-layer?

    Again, no, not really. The term base-layer tends to be used when considering more technical layering or higher-output activities like running, climbing, or backcountry skiing. Thermal underwear tends to be referenced with activities like resort skiing or hiking. But both terms essentially describe the same thing: the layer closest to your skin.

Why Trust TripSavvy

Nathan Allen is TripSavvy’s Outdoor Gear Editor. He hates being cold but loves outdoor activities like backcountry skiing, snowshoeing, and running in the cold. So he’s very obsessive about his layering. Nathan has loved Smartwool’s 250 layers for a long time. But he will also frequently seek out Patagonia’s Capilene line and anything from Ibex and Minus33. Above all, he appreciates merino wool and tends to opt for it, mainly for its stink-blocking chops.

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