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.

base-layer-bottoms

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.

base-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.

base-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.

base-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.

base-layer-tops

Comfy as you warm up, as you cool down and 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.

base-layer-tops

First half-mile cold; next 3 miles sweaty; lunch break cold. Don't stress—the REI Co-op lightweight half-zip long-sleeve base layer wicks and breathes to keep you comfortable all day.

base-layer-tops

The women's REI Co-op lightweight half-zip base layer top wicks and breathes to keep you comfortable hiking or skiing as you go from cold to warm to overheated and back.

base-layer-tops

The women's plus-size REI Co-op lightweight half-zip base layer top wicks and breathes to keep you comfortable cold-weather hiking or skiing, as you go from cold to warm to overheated and back.

base-layer-tops

The men's REI Co-op lightweight long-sleeve base layer crew keeps you warm until you warm up, then wicks sweat to keep you comfortable when you're going hard.

base-layer-tops

What could possibly keep you warm until you warm up, then keep you comfortable when you start sweating on the trail? The men's tall REI Co-op lightweight long-sleeve base layer crew is what.

base-layer-tops

Comfy as you warm up, comfy as you cool down, even comfy when you break a sweat—the women's REI Co-op lightweight long-sleeve base layer top is ideal for skiing, hiking and lunch break, too.

base-layer-tops

The women's REI Co-op long-sleeve lightweight base layer crew top wicks, breathes and stretches for comfort through every temperature change as you hike or ski the day away.

base-layer-tops

The REI Co-op lightweight base layer zip-neck top in men's tall sizes knows how to keep you comfortable through a whole day of changes from cold to warm to sweaty and back to cold again.

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