The Pines Microgrid Ultra-Lt Baselayer Crew Top runs on a synthetic microgrid fabric built to do what wool does, minus the weight. The grid construction traps warmth against the skin while wicking properties pull moisture away, so we stay dry and regulated whether we're climbing hard or standing still at the top. It's an ultralight alternative that never asks us to choose between packability and performance. What Our Gearhead(R) Experts Are Saying:"No zip to fuss with, no hood to adjust, just thumbholes and a slim fit that disappears under everything else I've got on."