This slim and lightweight ActionHeat 5V Rechargeable Battery Men's Heated Vest Liner delivers soothing warmth to your core body and can be worn over another garment and under a jacket. Equipped with the powerful FAR infrared heating and ActionWave heat reflective technology system, this heating vest liner has 3 built-in heating panels strategically placed on the chest and upper back to warm your body. This heated body warming vest liner can be charged with a power bank and activated by pressing and holding the button control. You can also adjust the temperature for desired heating with its 3 heat settings. This heat liner features 100% polyester interior and nylon exterior for a soft feel and durability. Wear this liner vest underneath your jacket and over a base layer or shirt when it's cold outside, especially during early morning starts, cool evening motorcycle rides, hunting, fishing, outdoor working, etc.