Product Information Features: High conversion efficiency, energy saving, the average hour with one degree of electricity. Easy to cut to the size you need. Applicable to various shoe types. Make your foot more comfortable and warm. Removable design, convenient and clean. USB charger,connected to PC, laptop,charger, keep your feet warm indoor. Specifications: Color: Black Material: Carbon Fiber Function: Foot Warmer Applicable Gender: Unisex Maximum Voltage: 4.5V Heating Range: Within 35 Shoe Line Insole Thickness: 4mm / 0.20'' (appr.) Package Includes: 1 Pair X Heated Insoles 1 X USB Cable How long does the insole get hot? Answer: The heating time is determined according to the product with power storage function. This product does not have a power bank and can only be plugged in to generate heat. If you use a power bank yourself, make sure that the power bank output is above 5V/2A.