The bottom of the drink coaster is made of food grade silicone. It can be heated any drink with flat-bottomed container. It will keep your drink warmer through USB port. Keep your hot coffee, tea, or other beverage warm by USB Device. It is suitable for mostly kinds of cup shapes. Mini warmer plant for keeping your hot coffee and tea warm long as you wish. Magic helper for you in home or office in daily life. Welcome to your customization! 3.74″ L x 3.74″ W x 0.24″ H