Men's innerwear, long sleeves, autumn and winter, inner shirt, round neck, thermal, heat-generating, warm, Tech Thermo, work, for work, gray, BT Thermo Inner Shirt Long Sleeve Round Neck Generates heat by reacting to the moisture of the human body! Not only does it provide warmth, but it also uses special rayon with the latest technology that has a heat-generating effect. The fibers react to moisture such as steam constantly emitted from the human body and quickly generate heat, which also lasts.