This mug coaster is light weight and compact size. It is made of ABS and Aluminum Alloy. The cup heating set is used to heat the cup, keeping the water, coffee, milk and tea in cup at a constant temperature around 50 degrees Celsius to maintain a good taste. It is designed to disconnect and prevent automatically the battery from overcharging when your phone is fully charged. It is light weight and compact size, easy to carry and stoge.