Ultra 10 Core with 2 Ply, Polyester Š—– Metalized Polyester. It is perfect for venting and exhaust applications. Do not use for the venting of cooking and clothes drying Appliances unless approved and recommended by the appliance manufacturer. The outer layer of this polyester film is also metalized for aesthetics. UL Rated Operating Temperature: -20ÎçF up to 180ÎçF, -29ÎçC up to 82ÎçC. 25 feet.