X BIONIC Men Invent 4.0 Light Singlet T shirt Arctic White/Opal Black, Small

This under layer for warm weather uses thermoregulation to counteract the risk of overheating When worn directly on the skin, it produces its climate-control effect The integrated, patented and award-winning 3D Bionic Sphere System cools you when you perspire and warms you when you're cold Model Number: IN-YT01S19M