Our outdoor expertise doesn't stop at zip-off pants. The men's REI Co-op Everyday briefs are built to run trails and traverse mountains—or sit super comfortably while you plan those things.

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An ideal base layer for getting vert or counting off switchbacks, these men's Artilect Flatiron 185 leggings provide soft, breathable warmth while you explore outdoors.

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An ideal base layer for getting vert or counting off switchbacks, these women's Artilect Flatiron 185 leggings provide soft, breathable warmth while you explore outdoors.

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Kari Traa Floke base layer pants blend fine merino wool with tech fibers to create a soft, medium-weight fabric with good warmth, natural odor resistance and breathability for cold-weather activities.

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Great for wearing under other layers, the women's Kari Traa Fryd base layer pants feature a supersoft, quick-drying material that moves with you and cuts out chafing so you can get out exploring.

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When you're giving it all you've got, you need layers that work with you. The women's Kari Traa Fryd base layer pants dry fast, stretch with your body and reduce chafing.

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From trekking in Thailand to traversing tough terrain in Baja, ExOfficio has spent decades perfecting the art of adventure—and underwear. Here are their Give-N-Go 2.0 Full-Cut briefs for women.

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Harnessing the warming power of Heatwave™ technology, the men's Seirus Heatwave Lite Reversible base layer bottoms reflect heat back to your body, and are now available in a lighter-weight design.

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Harnessing the amazing warming power of exclusive Heatwave™ technology, the men's Seirus Heatwave Reversible base layer bottoms reflect heat back to your body to keep you warm on cold-weather outings.

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Built for a wide range of sports and outdoor activities, the Saxx Hot Shot boxer briefs come equipped with highly breathable, quick-drying DropTemp™ tech to keep you cool when temps are high.

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Laser-cut for a clean finish and barely-there feel, the sleek Kari Traa Idunn Hipster underwear fit well under your workout tights. They also give 4-way stretch and dry quickly for functional comfort.

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Designed to layer under pants or shorts, the men's Smartwool Intraknit Active base layer bottoms help with temperature regulation and moisture management to keep you comfortable while you're active.

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Designed to layer under shorts or pants, the women's Smartwool Intraknit Active base layer bottoms help with moisture management and temperature regulation to keep you comfortable while you're active.

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Stay comfortable on cooler-weather adventures in the Smartwool Intraknit Thermal Merino men's 3/4-length base layer bottoms, which have a performance-enhancing design and a shorter, versatile length.

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