HOW TO USE: Power Up - Charge the provided ActionHeat 5-Volt batteries. Plug-In - Connect the batteries to the USB cords located in the pocket on the side of the boot. Turn On - Press and hold the touch-button control on the sock for 3 seconds. Press the button to cycle through the heat settings DESIGN: Polyester fabric blocks the cold out and keeps the warmth in Designed to be worn inside or outside Powered by rechargeable 5V batteries and can last up to 5 hours Three heat level settings Weather-resistant Turn off LED ghost-mode MAXIMUM HEATING TIMES: High: 145degF - 3.5+ Hours Medium: 130degF - 4+ Hours Low (Blue): 115degF - 5+ Hours