Flex-Vent KP Is A Strong Polyester Film Laminated and Encapsulating A Heavy, Corrosion Resistant Steel Wire Helix, Forms the Inner Core and Supports A Thick Blanket Of Fiberglass Insulation Over A Fiberglass Scrim. The Outer Vapor Barrier Has A Jacket Of Durable Black Polyethylene. Designed For Low To Medium Pressure Systems.