UL 181B-FX Listed cloth duct tape used in the HVAC industry to seal, seam, and join Class 1 Flex Duct systems, HVAC applications, installing air ducts and air connectors, and making connections and splices trouble-free and professionally-done. For use when the tensile strength and adhesion to stainless steel and polyethylene must meet or exceed the strict requirements of UL, flex duct manufacturers and city/state building codes.