The ultimate winter jacket somehow combines warmth with light weight, the feeling of freedom with full protection, waterproof fabrics with breathability. With the functionality of Castelli's Alpha construction. Polartec NeoShellPolartec NeoShell is the world's most breathable waterproof fabric technology. For years the outerwear industry has prioritized excessively high waterproof ratings that sacrifice the breathable performance needed during physical activity. NeoShell provides the strength and durability of a weather protective fabric, while still allowing dynamic air exchange and comfortable full range of motion. Polartec AlphaPolartec Alpha was invented for the U.S. special forces. They required a superior insulation system for extreme temperature variations and the start-stop conditions of combat. Alpha active insulation is engineered for consistent warmth, while allowing greater breathability during activity. This air exchange technology creates sustained comfort without shedding layers, which isn’t an option during a mission.