This electronic USB heating coaster is made of iron and aluminum with a felt bottom. The size is 4″ x 4″ x 0.6″. It’s voltage is 5V and power is 5W. Plug it into a USB socket to keep the temperature of your coffee, tea or other hot drinks below 80 degrees Celsius, without worrying about high temperature and high oxidation, safe to use. Universal size, easy to carry, suitable for most stainless steel cups, feeding bottles, ceramic cups, glasses, etc. Perfect for home and office use! The price includes the shipping cost to ca, QTY over 5000pcs by ocean. We are so confident in the quality of our product. Reach out to us if there’s ever anything you need; we are dedicated to your satisfaction.