The Under Armour Tactical Crew Base Layer Shirt utilizes ColdGear Infrared® technology to hold in body heat without adding weight or bulk. This base layer features dual-layer fabric with an ultra-warm, brushed interior and a smooth, fast drying exterior. The 4-way stretch construction allows for better mobility in every direction. With a thermo-conductive inner coating and sweat-wicking material, this long sleeve shirt will keep you warmer longer for workouts in the bitter cold.