The Marmot Men's Isotherm 1/2-Zip Jacket's Polartec Alpha insulation redefines comfort for hardworking alpine climbers and ski tourers. Unlike most breathable forms of insulation that start breathing after you're sweating, Polartec Alpha's air permeable insulation starts breathing the moment you put it on. Alpha also feels light and lofty like down even though it's a protective synthetic. Marmot wrapped windproof and extremely durable Pertex Quantum around this insulation for long-lasting performance at high altitudes. Angel-Wing Movement ensures freedom of movement whether you're climbing up or skiing down mountains.