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The Best Ultralight Merino Base Layer Ibex Woolies Pro Tech Crew Read more $115

Ibex (Women's)

Best Midweight Base Layer Icebreaker Merino 200 Oasis Thermal Top Read more $105

REI (Men's)

The Best Heavyweight Base Layer SmartWool Classic Thermal Merino Base Layer Read more $115

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The Best Base Layer for Extreme Cold Minus33 Heavyweight Yukon Thermal Long Sleeve Read more $150

Minus 33 (Men's)

Base layers, thermal underwear, long johns—whatever you want to call them, nothing in the process of layering clothing for warmth is as important as the layer that touches your skin. This layer has to do double duty, insulating you but also allowing heat and moisture to pass through it and out, away from your body.

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