The Capilene Thermal Weight Crewneck uses Polartec Power Grid fabric, a grid-patterned construction that holds warm air close to the skin while channeling moisture out and away. HeiQ Pure treatment keeps it fresh through repeat wear, and the smooth face slides cleanly under a shell or fleece without adding bulk. What Our Gearhead(R) Experts Are Saying:"I've worn this as my go-to baselayer for cold starts and long days where I'm working hard. It traps heat without feeling bulky, and it breathes well enough that I don't feel clammy when the pace picks up."