How does ActionHeat's Tri‑Zone Heating system work in base layer shirts?

ActionHeat's base layer shirts use a powerful Tri‑Zone heating system. There are three built‑in heating panels strategically placed on the chest and upper back to warm your core body temperature. When you first get your shirt, fully charge the power bank with the supplied charger, plug it into the USB plug in the pocket, and press and hold the touch‑button controller on the chest for three seconds to turn it on. The touch‑button lets you choose from three heat settings-high, medium and low-and four LED indicators show the battery's remaining charge. This system provides flexible warmth without adding bulk, so you can wear the shirt as a base layer for winter sports or under everyday clothing.