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

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Harnessing the warming power of Heatwave™ technology, the men's Seirus Heatwave Lite Reversible Long-Sleeve base layer top reflects heat back to your body, and is now available in a lighter design.

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Harnessing the warming power of Heatwave™ technology, the men's Seirus Heatwave Reversible Long-Sleeve Crew base layer top reflects heat back to your body to fend off winter's chill.

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Pack less and do more with the men's Mons Royale Icon Raglan top. You'll go from bike laps to alpine climbs and everything in between without having to change shirts.

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With mesh ventilation for cooling, minimal seams to help reduce chafing and a fit that moves with your body, the men's Smartwool Intraknit Active base layer top is ready to go the distance with you.

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With mesh ventilation for cooling, a fit that moves with your body and minimal seams to help reduce chafing, the women's Smartwool Intraknit Active base layer top is ready to go the distance with you.

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Engineered 3D-knit panels of Merino Sport yarn deliver perfectly placed breathability and thermoregulating comfort on the women's Smartwool Intraknit Thermal Max Merino Pattern hoodie.

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With merino comfort, ventilation and articulated flex zones, the Smartwool Intraknit Thermal Max Quarter-Zip base layer top will be what you grab first for high-intensity, cold-weather adventures.

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With seamlessly integrated insulation and ventilation and articulated flex zones, the women's Smartwool Intraknit Thermal Max Quarter-Zip base layer top is made for high-intensity, cold-weather fun.

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Adventure all day in the cold with the enhanced breathability of the men's Smartwool Intraknit Thermal Merino Colorblock Crew base layer top, designed with body-mapped mesh and distinctive patterning.

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Keep your temperature just right on cold days with the built-in ventilation of the men's Smartwool Intraknit Thermal Merino Colorblock Quarter-Zip base layer top featuring body-mapped mesh zones.

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Keep your temperature just right on cold days with the built-in ventilation of the women's Smartwool Intraknit Thermal Merino Colorblock Quarter-Zip base layer top featuring body-mapped mesh zones.

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This minimalist Smartwool Intraknit Thermal Merino crew base layer top is anything but insignificant. It's a lightweight, super-moveable top perfect for all of your sweatiest cold-weather activities.

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This minimalist Smartwool Intraknit Thermal Merino women's crew base layer top is lightweight and super-moveable—perfect for all of your sweatiest cold-weather activities.

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