This 4 inch diameter wide hood mouth hood is contractor grade, heavy duty construction that has a limited lifetime warranty. The hood louvered dampers operates quietly for maximum exhaust air flow and seals when not in operation to help prevent back drafts. The dryer vent hood has a melting point of 325 F. The dryer hood is flexible, easy to install. The dryer vent should be self-cleaned with wind or rain. The dryer duct's bird guards helps prevents birds and rodents from entering home through your dryer vent.