MHP-25 (25' length) flexible duct is constructed with a spring steel wire helix, encapsulated in a 2-ply, air tight inner-core. Fiberglass (Choice of R4.2, R6, R8) insulation encompasses the core and a unique metalized, reinforced vapor barrier surrounds the entire duct. Available in cartons and poly-bags. Features and Benefits: UL listed and labeled Guaranteed out of package lengths 10 year limited warranty Greenguard Certification Formaldehyde free 3/8" oversize inner core Certified R-Values.