Naturally odor-resistant with mesh ventilation to help prevent you from overheating, the women's Kari Traa Lam base layer pants have a supersoft feel for next-to-skin comfort in any season.

Underwear BottomsBase Layer Bottoms

A go-to base layer for winter play, these Kari Traa Lam base layer pants are a supersoft, supersmooth pair of merino wool leggings with ergonomic lines for a pro-sport look.

Underwear BottomsBase Layer Bottoms

Spun from superfine merino wool, the women's Kari Traa Lam long-sleeve base layer top is exceptionally soft, smooth and breathable for easy layering year-round.

Underwear TopsBase Layer Tops

With its stretchy, supportive and quick-drying fabric, the prAna Lanya bra keeps you moving through workouts, yoga sessions and warm-weather hikes.

UnderwearSports Bras

Made with a brushed feel for easy comfort, the Marmot Leda sports bra is ideal for morning spin classes, afternoons at the climbing gym, and any other low-impact workout.

UnderwearSports Bras

Make your first layer a comfortable one with the men's Picture Organic Clothing Lhotse base layer pants. They feature chafe-free seams and a nonirritating elastic waist band.

Underwear BottomsBase Layer Bottoms

Combining a warm, breathable 100% merino wool exterior with a 100% LIFA® wicking interior, the women's Helly Hansen LIFA Merino Midweight crew top is the perfect base layer for cold-weather pursuits.

Underwear TopsBase Layer Tops

Fend off the chill and stay out longer in the men's Helly Hansen Lifa Merino Midweight base layer pants. Built for winter fun, they blend merino wool with technical fabric to keep you cozy and warm.

Underwear BottomsBase Layer Bottoms

Layer up for sledding, skating or shredding in the men's Helly Hansen Lifa Merino Midweight Crew base layer top. Its 2-layer construction combines cozy merino wool with durable technical fabric.

Underwear TopsBase Layer Tops

These REI lightweight base layer bottoms are designed to keep you warm and wick away moisture during high-performance outdoor activities when the temperature starts to drop.

Underwear BottomsBase Layer Bottoms

From morning's first frosty steps to midday sweat and exhilaration, the men's REI Co-op lightweight base layer bottoms wick and breathe to keep you comfortable all the way.

Underwear BottomsBase Layer Bottoms

The men's REI Co-op lightweight base layer bottoms wick and breathe to keep you comfortable from the first cold steps of morning to sweaty exhilaration on the trail hours later.

Underwear BottomsBase Layer Bottoms

Heading out to play hard? The REI Co-op lightweight base layer crew top keeps you warm until you warm up, then wicks sweat to maintain your cool when you're charging.

Underwear TopsBase Layer Tops

Comfy as you warm up, comfy as you cool down, comfy when you break a sweat. The women's REI Co-op lightweight base layer top is ideal for hiking, cycling and even sleeping—especially in the summer.

Underwear TopsBase Layer Tops