The Ideal-Airâ„¢ Supreme Silver/Black Flex Ducting is a high-quality, 3-ply aluminum foil duct. The duct has a black interior core and a silver reflective exterior. 100% made in the USA, this ducting is constructed with a spring steel wire helix, which is then encapsulated in a polyester, aluminum foil and polyester tri-laminate. Specifically oversized by 3/8 in to fit any application. Duct length is 25 ft and includes 4 zip ties per bag.