Hard pitches on a cold alpine route heat the body fast, and the Switch Base Zip T is the fast-drying base layer that moves that moisture off the skin. Octayarn warp-knit fabric uses hollow, cog-shaped fibers to trap warm air and wick moisture, with no face or lining fabric layered over it. That makes the top a cold weather base layer for alpine climbing, mountaineering and ski touring. What Our Gearhead(R) Experts Are Saying:"On ski tours, I opened the deep front zip on steep skin tracks to vent the heat. By the time I zipped it back up at the top for the descent, the top had dried and held its warmth."