A heat transfer material comprised of a polymeric material and a nitride or oxide is provided and is thermally conductive, but electrically non-conductive. The polymeric material may be silicone rubber, and the nitride or oxide may be aluminum nitride, boron nitride, silicon nitride, aluminum oxide or beryllium oxide. The material is made flexible by adding plasticizer and remains flexible after an extended period of use. A dielectric jacket for an electrical heating cable is thermally conductive and remains flexible so that it can be reused. The heat transfer material can be used on heating devices such as steam tubes and panels, where the heat transfer material does not bond to or adhere to the heated surface, which allows the heating device to be reused.