Designed for wherever UL-181 standards for Class 1 air duct is required. 2-ply polyester laminated inner core provides outstanding resistance and durability. Fiberglass reinforced metalized outer jacket is extremely strong and will not unravel. Suitable for use with heating, ventilation and air conditioning systems. R-4.2 silver. Features The 2-ply polyester laminated inner core provides outstanding resistance and durability The fiberglass reinforced metalized outer jacket is extremely strong and will not unravel