Product Description: Connect the USB cable to the computer or 5V charger switch interface, coasters begin to generate heat.The need for thermal insulation on the silica glass coasters, then it can play the role of insulation (please don't use the recessed bottom cup, glass Cup is best) Please do not use this insulation Cup for outside functions. Please Unplug the USB cable when don't use, to extend the life of the product. It is only used to keep your tea or coffe warm,but not for heating. Specifications: Material: Silicone+Carbon fiber Color: Blue, Green, Red Size: 9.5x0.6cm Power: 3.75W Voltage: DC 5V Current: 750MA Package included 1 x USB cup warmer