Our cup warmer is powered by DC 5V USB plug, with a ON/OFF switch and power indicator and 4 USB hubs, the middle part is the heated aluminum sheet, used to keep hot tea, water and coffee drinks at a certain temperature(about 86-104Fahrenheit). Light weight, compact size, easy to carry, suitable for most stainless steel cups, baby bottles, ceramic cups, glass cups, etc. Perfect for promotion, advertising, gift giving, etc. 4.06" L x 3.66" W x 0.87" H