Additional Details ------------------------------ Product description: ATCO #030, 036, and 031 are UL 181, Class 1 Air Ducts and are manufactured with a tri-directional fiberglass scrim reinforced, metallized polyester outer jacket. The inner core of all three products is air-tight and designed for low-to-medium operating pressures in HVAC systems. ATCO #036 and 031 have increased insulation for superior thermal performance. ATCO Insulated Air Duct, Double-Ply Flexible, Series: 036, 5 in Inside Dia, 25 ft Length, 5000 fpm, 0.05 perms Vapor Transmission, 10 in WG, Metallized Polyester Jacket, Silver, Domestic