Their best-selling ultralight and ultra-packable windbreaking layer for zipping up the trail, to the crag, or wherever fast-paced pursuits call for maximizing movement and minimizing weight. The Pertex® Quantum Air fabric sits super-light on the skin, remaining breathable while cutting through alpine gusts and rebuffing light moisture. When conditions ease up, it quickly packs down into a discreet internal pocket. Call it an ultralight softshell or a super breathable wind shirt, but we just call it the do-it-all stretch layer that lives in their pack until the moment strikes.