Best Thermal Underwear for Getting Active: UA Base 2.0 Leggings

Under Armour was among the first on the scene when it comes to athletic leggings. And while there are plenty of active thermal bottoms that max out on engineering, crafted with articulated flatlock seams and futuristic fabrics, Under Armour has stuck to a more straightforward approach. Namely, uncomplicated, but high-performance materials, and a great fit.

The combination of a featherlight fabric and four-way stretch make these an extremely comfy pair on their own, but they work especially well when you’ve got an intense mobility workout ahead of you. While they’re great at insulating your body heat, they’re not suffocating. The material is still breathable and moisture-wicking so you can bank on hitting the gym without your leggings holding you back.

Best Era-Authentic Thermal Underwear: Hemen Ikar Long Johns

These are the thermal underwear your favorite style icons would have worn—if they had any sense. The French undergarments label Hemen channels old-school craftsmanship so authentic you’d half-expect to find these in a 1940s military surplus catalog (right next to a tin of mystery rations).

Made from organic cotton with a 2×2 ribbed jersey knit. These long johns may look like they’ve time-traveled from decades past, but they deliver modern-day comfort. And those three front buttons? A vintage-inspired touch that’s not just for show—they make getting in (and, more importantly, out) of these thermals a breeze.

Best Thermal Underwear for the Outdoors: Arc’teryx Rho Heavyweight Tights

Arc’teryx somehow sits at the crossroads of “cool guy flex” and “serious outdoor gear,” and naturally, they’ve found a way to make thermal underwear look downright wearable on its own. Their heavyweight Polartec pants, feature patented Power Stretch fabric that moves with you—so you get warmth without the feeling of being shrink-wrapped.

The exterior is a soft, durable nylon, while the interior boasts a smooth brushed fleece that traps heat and wicks away moisture. And the best part? A small thigh pocket, perfect for stashing your lip balm or headphones while you’re catching your breath on the slopes (or just flexing at the après-ski lodge).

More Thermal Underwear We Love

What to Look for in Thermal Underwear

Long johns aren’t really about making a statement, so colors and patterns don’t matter too much. What does matter, though, is fit and material. For maximum warmth retention, thermal undies should be snug but not overly restrictive. Oh, and flatlock seams are a must to prevent chafing; that should be non-negotiable.

When it comes to fabric, cotton is always a safe bet, but it absorbs moisture, which can actually make you colder. Synthetic blends—polyester, nylon, spandex—are quick-drying and durable, but have a bad habit of trapping odors. Merino wool, on the other hand is soft, moisture-wicking, naturally odor-resistant, and keeps you warm without adding bulk—and it’s one of our go-to winter fabrics for those exact reasons.

Bottom line? Shimmying into a pair of thermal undies on a freezing day should feel like unlocking a level of toasty the lesser-equipped masses can only dream of.

How We Test and Review Products

Style is subjective, we know—that’s the fun of it. But we’re serious about helping our audience get dressed. Whether it’s the best white sneakers, the flyest affordable suits, or the need-to-know menswear drops of the week, GQ Recommends’ perspective is built on years of hands-on experience, an insider awareness of what’s in and what’s next, and a mission to find the best version of everything out there, at every price point.

Our staffers aren’t able to try on every single piece of clothing you read about on GQ.com (fashion moves fast these days), but we have an intimate knowledge of each brand’s strengths and know the hallmarks of quality clothing—from materials and sourcing, to craftsmanship, to sustainability efforts that aren’t just greenwashing. GQ Recommends heavily emphasizes our own editorial experience with those brands, how they make their clothes, and how those clothes have been reviewed by customers. Bottom line: GQ wouldn’t tell you to wear it if we wouldn’t.

How We Make These Picks

We make every effort to cast as wide of a net as possible, with an eye on identifying the best options across three key categories: quality, fit, and price.