14" X 25' Insulated Flex Duct 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 is a jacket of durable black polyethylene. Designed for low to medium pressure systems. CODES/STANDARDS: Listed and labeled by Underwriters Laboratories, Inc., as a Class 1 Air Duct, Standard 181. It complies with the latest NFPA Bulletins 90A and 90B. Meets FHA and other U.S. government agency standards. Flame spread: not over 25. Smoke developed: not over 50.* INSULATION: R-4.2 VAPOR BARRIER PERMEANCE: .1 Perm per ASTM. Method E96, Procedure A. TEMPERATURE RANGE: 20 F to 250 F. EXTERIOR FACING AND VAPOR BARRIER: Polyolefin film, flame resistant *we recommend that you check with the local code body having jurisdiction in your area to determine applicable codes.