Don't underestimate the power of a well-engineered midlayer like the Mountain Hardwear Airmesh 1/4 Zip Top. Constructed from a unique active mesh Teijin fabric with a brushed backer that effectively moves sweat away from your skin, the Airmesh 1/4 Zip Top works constantly to regulate your temperature whether you're sucking air on the final summit push or resting at basecamp.