Dundas Jafine BTD420ZW ProFlex UL listed Dryer Transition Duct, 4-Inches by 20-Feet 4" x 20' Length Flexible Ducting UL 2158A listed product (not marked) for clothes dryer transition duct if used in lengths of 8' or less Ideal for both gas and electric dryers applications, bathroom fans, and other exhaust Heavy duty 4 ply construction