Waterproof design: The cup warmer for desk was covered with a layer of thermal conductive glass without need for security concern for occasional spill and it is easy to clean,safe and reliable. Suitable for most cups: The Smart coffee warmer has 4.4Inch diameter heating area. It can be fit most cups, such glass cup,stainless steel cup, Ceramic cup etc. for better results, we recommend using flat bottom glass cup or stainless steel cup. Placing a lid over the mug also help retain heat. Maintain optimal temperature: This mug warmer not only can the cooling speed of hot coffee, But also can heat your coffee up to (55-65-75℃). and keep this temperature whole day, which is neither too hot nor too cold, you can sip your coffee at any time, without waiting. Safe & Reliable: Thanks to the microgravity technology, this coffee cup warmer can shut off/on auto. Just plug the adapter into outlet, then put your mug on and the coffee warmer work auto, take it away, the cup warmer off auto. Winter's Gift: keep the beverages(Coffee, tea, milk etc) warm whole day, making it a great gift for lover, dad, mom, wife, husband, grandparents and all your loved on Valentine's day, Thanksgiving and Christmas, and other special occasions to express your sincere care.