Lambro’s 4 In. x 25 Ft. UL 181 Class 1 Air Connector is a flexible aluminum/aluminum foil flex duct. It is ideal for applications where building codes require use of all aluminum duct. The duct has a maximum operating temperature of 250 deg.F. Ideal installations include bathroom fan venting and general exhaust applications. Please note the UL listing on this product is for installations of 14 ft. or less. This duct is not to be used when venting a dryer’ as a UL 2158A transition duct is required for that application.