What type of venting material is required for installation?

You must use only rigid metal or semi-rigid metal 4-inch diameter ductwork for venting the dryer. Do not use plastic or flexible foil venting materials, as these are known to collapse, be easily crushed, and trap lint, which obstructs airflow and increases the risk of fire. If a flexible metal transition duct is needed between the dryer and the wall connection, only a UL-listed flexible metal transition duct may be used for that short section. (Pages 5–6, 14–15)