The Lambro foil flex 4-inch x 25-foot UL 2158A transition duct is ideal for venting an electric or gas clothes dryer to the wall pipe. The transition duct is for new and replacement clothes dryer installations. The foil flex duct is highly flexible, allowing tight bends for easy installation. When installing the duct, you can cut it to length to allow for stretching for maximum airflow. The duct manufacturing material is aluminum and polyester over a galvanized wire helix frame. The certified UL 2158A duct contains a UL marking on each length. Please be sure to check local building codes before installation.