The women's REI Co-op lightweight base layer tights keep your comfort level high from the first cold steps of morning to the sweaty joy of working your way up a steep trail.

Underwear BottomsBase Layer Bottoms

The women's plus-size REI Co-op lightweight base layer tights warm you in the morning chill, then wick and breathe to keep you cool as you work your way up a hot afternoon trail.

Underwear BottomsBase Layer Bottoms

Layered under a pair of pants or on their own, these women's Smartwool Merino 150 Lace base layer bottoms are just the thing for an afternoon of snowshoeing or cool-weather hiking.

Underwear BottomsBase Layer Bottoms

Just as beloved while sweating on the trail as sleeping in the tent, the ultrafine merino wool of the women's REI Co-op Merino 185 base layer bottoms is soft, breathable and naturally odor resistant.

Underwear BottomsBase Layer Bottoms

Just as beloved while sweating as while sleeping, the ultrafine merino wool of the women's REI Co-op Merino 185 base layer bottoms is soft, breathable and naturally odor resistant.

Underwear BottomsBase Layer Bottoms

Warm merino bottoms for the coldest months, the women's Icebreaker Merino 260 Tech High Rise base layer leggings are great for winter layering on skiing, snowshoeing or other cold-weather adventures.

Underwear BottomsBase Layer Bottoms

Keep the winter chill away with the women's Icebreaker MerinoFine base layer leggings, which feature a high waist for added coverage—and its merino wool is naturally stretchy and odor resistant.

Underwear BottomsBase Layer Bottoms

Start with a high-performing next-to-skin layer and take advantage of the snow. The women's REI Co-op Midweight Base Layer Tights have a smooth face for easy layering and brushed interior for warmth.

Underwear BottomsBase Layer Bottoms

Hit the lifts with all you've got. The women's Burton Midweight X base layer pants move right along with you with breathable, quick-drying fabric—plus, a media port stashes your phone for easy access.

Underwear BottomsBase Layer Bottoms

Crafted in a quick-drying mixed fabric blend that wicks moisture away from your body when the intensity rises, Kari Traa Perle base layer pants are a 4-season favorite.

Underwear BottomsBase Layer Bottoms

Built for cold, on-the-move days, the women's Arc'teryx Rho Heavyweight base layer bottoms are highly stretchy and pair a durable, smooth face with a soft, brushed interior for warmth and wicking.

Underwear BottomsBase Layer Bottoms

On cold days with lower output, layer up in the women's Arc'teryx Rho Lightweight base layer bottoms. Made for wicking and warmth, they dry quickly, let skin breathe and deliver soft-brushed comfort.

Underwear BottomsBase Layer Bottoms

With beautifully detailed patterning and a soft merino wool fabrication, Kari Traa Rose base layer bottoms go beyond basic and are perfect for cold-weather activities.

Underwear BottomsBase Layer Bottoms

Whether under your hiking kit or just under jeans around town, the women's REI Co-op Silk bottoms make a great foundation as temps start dropping.

Underwear BottomsBase Layer Bottoms