Freeheart-Signature tumblers are durable; thermal insulated, and designed to last a lifetime. We create our tumblers using two layers of the highest grade polymer. It is the same product that is used to make prescriptive lenses. The tumbler is a double walled construction with one glass fitting in the other. The two are then ultrasonically welded to form your thermal insulated tumbler. The air trapped between the layers keeps your cold drinks really cold and your hot drinks hot for an extended time. This design virtually eliminates sweating and makes the tumblers extremely durable and shatter proof. In short, Signature Tumblers are the perfect glass for the car, patio, boat, and general entertaining, wherever the location might be. These tumblers show up almost everywhere and are always loved.