Enjoy a heartfelt cup of coffee in this Double Double Sweetheart Coffee Mug! Made with a double layer of mouth-blown borosilicate glass, each glass will keep hot and cold drinks insulated while the outside surface will remain comfortable in your hands. Two layers of this glass are used to give it ample insulation, style, and to create an optical illusion. The glass creates an effect where the drink appears as though it is 'floating' within the glass. When filled with your favorite beverage, the unique design of this heart coffee mug will be 'lovely' to the eye. These mouth-blown glasses are an exciting product for any home, restaurant, and café.