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.

Underwear TopsBase Layer Tops

When it comes to base layers, basic is better. The men's Lole Logan base layer bottoms are perfect under your gear for outdoor training or activities, or for everyday life.

Underwear BottomsBase Layer Bottoms

When it comes to base layers, basic is better. The men's Lole Logan half zip is a long-sleeve base layer top that's perfect under your gear for outdoor training or activities, or for everyday life.

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

Underwear BottomsBase Layer Bottoms

Soft, breathable and naturally odor resistant, the ultrafine merino wool of the men's REI Co-op Merino 185 base layer bottoms is beloved for sweating on the trail—and just sleeping!

Underwear BottomsBase Layer Bottoms

Hike, bike and even sleep in the men's REI Co-op Merino 185 short-sleeve base layer top. The soft, breathable and naturally odor-resistant ultrafine merino wool makes it an ideal next-to-skin layer.

Underwear TopsBase Layer Tops

Soft, breathable and naturally odor resistant, the ultrafine merino wool of the men's REI Co-op Merino 185 long-sleeve base layer top is beloved while sweating on the trail—and sleeping in the tent.

Underwear TopsBase Layer Tops

Soft, breathable and naturally odor resistant, the ultrafine merino wool of the men's REI Co-op Merino 185 long-sleeve base layer top is beloved for both sweating on the trail and just sleeping.

Underwear TopsBase Layer Tops

Soft and breathable, the ultrafine merino wool of the naturally odor-resistant men's REI Co-op Merino 185 long-sleeve half-zip base layer top is ideal for sweating on the trail—and sleeping in a tent.

Underwear TopsBase Layer Tops

The ultrafine merino wool of the men's REI Co-op Merino 185 long-sleeve half-zip base layer top is an ideal soft, breathable, odor-resistant layer for sweating on the trail—and sleeping in a tent.

Underwear TopsBase Layer Tops

Built with soft merino, the Icebreaker Merino 200 Sonebula Long-Sleeve High-Neck Thermal top regulates body temperature in all weather conditions while resisting odors. High collar adds coverage.

Underwear TopsBase Layer Tops

Stay dry on the trail in the soft, breathable and naturally odor-resistant REI Co-op Merino Boxer Brief Underwear for men. They're made to keep you comfy throughout the day.

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Stay dry on the trail in the soft, breathable and naturally odor-resistant REI Co-op Merino Boxers for men. They're made to keep you comfy throughout the day.

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Your underwear should deliver lasting comfort. Whether you're spending the day at work or a couple hours at the gym, Smartwool Merino Plant-Based Dye boxer briefs help you stay confidently comfy.

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