PR-25 (25’ length) flexible duct is constructed UL Listed & Labeled with a spring steel wire helix, encapsulated in a Guaranteed out of package lengths 2-ply, air-tight inner core. Fiberglass insulation 10 Year limited warranty choices of R4.2, R6 & R8 encompass the core and GREENGUARD Gold Certification a black polyethylene vapor barrier surrounds the Formaldehyde free (see www.jplflex.com for more info) entire duct. 3/8” oversize inner core Certified R-Values