6 Fave Thermal Undergarments: Your Winter Fashion Savior

It’s getting colder. I feel it in my fingers. I feel it stroking my bare legs; I’m still in denial. But I feel it in the cold, crackling leather of my car seats when I get in it, in the engine’s wheezy complaint when I start the ignition. Winter has come.

In the wirecutter.com’s quest to find the best women’s base-layer top and bottom for us, they sent seven testers skiing, running, rock climbing, cabin lounging, and more in 18 women’s tops and 17 bottoms for four months and here are the results:


The Smartwool Merino 150 Base Layer Pattern Long Sleeve is an all-around workhorse base layer: It fits great, stays in place, wicks while you’re working, and warms when you’re taking a break. What distinguished this top from other base layers in our test, though, was its comfort and fit. Our lankiest testers applauded its long sleeve and shirt length, which kept their wrists and backs covered. Testers also liked the shirt’s pinch-free, flattering design. The microweight fabric—made of merino wool fibers spun around a nylon core—was particularly soft, non-itchy, and durable compared with the competition. Despite having perhaps the lightest-weight fabric we tested (at 150 grams/m2), the Smartwool Merino 150 kept us insulated in every temperature, and was beloved among our weight-conscious traveling and backpacking testers.

Because the shirt was so thin, in our tests it felt more breathable (and dried more quickly) than other, similar wool layers. Heat and vapor were able to escape quickly during movement, especially compared with the Hot Chillys and Duofold base layers we tested. Testers noted that even after fall trail runs in Colorado or long, steep climbs in Southern California’s mountains, the Smartwool top breathed well and wicked away sweat, drying with uncharacteristic speed for a wool base layer. Because it breathed so effectively and offered UPF 30 protection, testers were able to wear this base layer as sun protection with the sleeves rolled down even on warmer days. It performed equally well layered under jackets for skiing in Colorado, and it stayed warm when it got wet in the moist Pacific Northwest.

The soft merino wool of the Ibex Woolies 1 Crew makes it feel like a luxury upgrade, but currently it’s only a little more expensive than our top pick, the Smartwool Merino 150. Our testers found the fabric softer and less itchy than that of the Smartwool top and loved that the Ibex shirt had one of the longest torsos of any base layer we tested, keeping the lower back nicely covered. The Woolies 1 Crew’s longer cut, ribbed pattern, and casual design make it just as suited for Colorado-style business meetings under a blazer as for hanging out in the lodge. It has a looser, sometimes baggy fit that stretches with wear, which in our tests sometimes required more care under backpack hip belts and climbing harnesses. While the ribbed knitting makes it more comfortable for everyday use, it looks more like an outdoor-lifestyle piece than a top you would wear for extreme activities.

The Cuddl Duds FlexFit Long Sleeve Crew is an attractive base layer that fits similarly to the popular Lululemon Swiftly Tech Long Sleeve Crew—a perennial ath-leisure activewear top—at half the price. Our testers loved the longer shirt length, but the Cuddl Duds top’s best feature is its long sleeves, which go past the back of the hand and come with (bonus!) thumbholes. In our tests, the stretchy, velvet-soft fabric kept the shirt from riding up during movement and made this top ultra-comfortable. However, the lightweight fabric of the Cuddl Duds wasn’t as warm as that of other layers, especially when it became moist from rain or sweat. Multiday backpackers and testers who did not wash it after a single wear complained of odor, too. It’s a good option for non-overnight activities like day hikes or an afternoon of climbing.

The Paradox Women’s 1/4 Zip Top Base Layer is special. It wicks, it warms, and it has a touch of merino at a fraction of the cost of the competition. This long-lasting mostly polyester blend is made of a heavier and thicker fabric than our other picks, but it worked well while we were trail running and backpacking to keep us warm in cool, dry climates. The biggest complaint was odor—it held on to stink after a day of sweating, unlike other tops in our test group. It’s not as breathable as the Smartwool and other wool shirts, and it takes longer to dry. And we didn’t love its outdoor-athletic style because it didn’t translate to casual settings. But after all our experience testing tops, we think Paradox might be one of the best-kept budget secrets in the outdoors world, and if the style and fit work for you, this top is an unrivaled performance bargain.


The Arc’teryx Rho LT Bottom is everything a pair of base-layer bottoms should be: soft, stretchy, warm, and resistant to shimmying down during activity. This pair doesn’t stick or rub when layered under pants, and best of all, it can work on its own because it isn’t see-through and has a flattering fit. The thick waistband stays up without digging into your belly or rolling over uncomfortably, and the fabric is soft and stretchy without the plasticky feeling of other synthetic base layers. These bottoms are so comfortable that when you get home from a day of play in the cold, you won’t want to take them off. Note that this is the first time we’ve recommended a piece of Arc’teryx gear; usually the company’s items are too specialized to be best for most people. But up until now, all the bottoms we’ve tried have had flaws, and this pair—it just doesn’t. We found it genuinely worth the cost for the fit. We had to pry it away from our testers. They really, really didn’t want to give it back.

The synthetic Hot Chillys Women’s Micro-Elite Chamois Tight almost mirrors the Arc’teryx Rho LT Bottom’s ability to move with you throughout the day, for about $20 less at this writing. These Hot Chillys tights aren’t as stretchy and don’t fit as well as the Arc’teryx bottoms, but they don’t ride up or down, which is more than we can say for almost every pair of women’s bottoms we’ve tried over the past two years.

The workhorse of base-layer bottoms, the Icebreaker BodyfitZone Zone Leggings were among the best of the bunch in our tests. We liked the fit, the mobility, and most of all, the breathability of this pair of bottoms. Plus, merino wool has natural anti-odor capabilities—and for us, it worked. The downside: Merino can be expensive, this pair isn’t as flattering, and it wears more like long underwear than an opaque legging.


The beauty of these thermal undergarments is that you can still wear your favorite clothes on winter without looking bulky with so much layers. Fashion doesn’t have to be impractical.  Any favorite brands of yours you’d like to spiel to us? Or other winter fashion tips maybe? We’d love to hear them, comment below!


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