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.

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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.

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Start layering your little ones with the toddlers' warm, breathable REI Co-op Lightweight Crew Long Underwear top. It features a made-to-move design and all of the comfy for a day of play.

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Start layering your littles with the kids' warm, breathable REI Co-op Lightweight Crew Long Underwear top. It features a made-to-move design and all of the comfy for a day of play.

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Layer your little one with the REI Co-op lightweight long underwear bottoms for infants and toddlers. Designed for warmth, these bottoms are easy to pull on and absorb moisture as it comes.

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Layer your hiking pal with the REI Co-op lightweight long underwear bottoms for kids. Designed for warmth, these bottoms are easy to pull on and wick moisture for comfort.

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Stay halfway to shred-ready by sleeping in the women's NRS Lightweight Union Suit. With midweight insulation and a dropseat for ease, this union suit is key to shoulder season adventures.

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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.

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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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With its buttery soft feel and support that's like a gentle hug, the girls' Athleta Long Distance bra might be her new favorite for school, practice and play.

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Designed with soft, supportive fabric that's great for school, practice and playground time, the girls' Athleta Long Distance 2.0 bra helps young adventurers keep moving in comfort.

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Great for yoga and training, the Vuori Longline Elevation bra features a dropped neckline, strap details and a wide, comfortable band.

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Providing lightweight warmth and natural temperature regulation, the Kari Traa Lucie Long-Sleeve base layer top is made from fine merino wool and designed to layer smoothly under your jacket.

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For support on hikes, rides and beyond, choose the Wild Rye Lucille sports bra. It provides reliable, distraction-free support, thanks to carefully placed seams that sit comfortably under a pack.

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