he fabric consists of brushed, micro-denier polyester fleece for lighter weight and greater strength and durability. But to ensure this men's thermal base layer top doesn't interfere with your active endeavors, we've placed stretch panels in key areas of this men's thermal zip-t layer for added maneuverability. A unique product for those demanding the warmest possible undergarment for winter or mountain sports, the La Montaña zip-t with thumb holes is guaranteed to keep you roasty and toasty. ME Chamois gussets under arms and at cuffs for a closer fit and increased performance Extended cuffs with thumb holes Zip pocket on the chest Zip through collar with interior wind flap for ultimate warmth Micro-denier polyester fibers for lighter weight, luxurious drape, breath-ability, strength and durability MTF polyester moisture transfer fibers for increased moisture management UPF 40 protection Mountain weight, active fit Warmth factor 10 out of 10 - Mountain weight for exceptional warmth in extreme conditions. Active fit - Designed to follow the body with a lighter feeling fit.