The Lambro flexible semi-rigid 4 inch x 8 foot UL 2158A clothes dryer transition duct is ideal for venting electric or gas clothes dryers. This duct connects one end to the dryer exhaust outlet and the other end to the pipe leading to the outside exhaust vent. Semi-rigid duct is preferred over foil flex as it does not collapse and is non combustible with a max operating temperature of 480°F. UL 2158A semi-rigid duct is recommend by most leading clothes dryer manufacturers.