GENERIC MEMORY TD450 4" X50' Proflex FOIL Duct ProFlex duct is ideal for many venting applications. Bulk 50' roll can be cut/sold to lengths needed for each job. Per UL2158A, only ducts 8' or less can be UL marked; only lengths of 8' or less can be UL approved for use as venting for gas and electric clothes dryers. ProFlex is constructed of heavy-duty, fire-resistant, 4-ply aluminum foil laminate that encapsulates a high-density, corrosion-resistant wire helix. This forms an airtight and easy-to-use air duct. This duct will not support combustion.