Class 1 insulated air duct UL/cUL 181.  Flexible helix core made of 2-ply polyester laminate and corrosion resistant galvanized wire.  Surrounded by a blanet of formaldehyde-free, fiberglass insulation that helps reduce heat and cool loss.  Jacketed by a heavy-duty, fire-retardant, silver polyethylene vapor barrier with reinforced scrim.