The Patagonia Capilene Lightweight Crew wicks sweat fast enough to disappear under a shell, thanks to a recycled polyester double knit treated with plant-based HeiQ Mint odor control. An underarm gusset and form-fitting cut open up a full overhead reach without binding at the shoulder. What Our Gearhead(R) Experts Are Saying:"I wore this under a windshirt on a fast trail run through cold morning air, and the thumb loops kept the sleeves in place through every arm swing."