The Hot Chillys Mec Blocking Zip-T features activated carbon woven into the yarns for extra thermal regulation in one midweight layer. Four-way stretch and flat seams let the fabric move with the body without chafing, and a quarter-zip collar vents heat fast when a climb heats things up. Micro-Elite Chamois construction keeps the fit smooth under outerwear while the brushed interior stays soft against the skin, run after run. What Our Gearhead(R) Experts Are Saying:"I wore this through a full day of lift laps without unzipping my shell once, cracking the quarter-zip instead whenever I started to overheat on the way up. By the last run it still smelled the same as when I put it on that morning."