Deflecto’s 4-inch Galvanized Steel Air Tight Vent Hood, Pipe, and Collar is suitable for venting a dryer or a bathroom fan. Made from steel to protect against corrosion, the fireproof ventilation accessory has a positive-action damper to improve efficiency and help keep cold air and rain from entering a home, according to Deflecto. We found it online for about $14. deflecto.com