100mm Backdraft Damper, One-Way Airflow Ducting Insert with Spring-Loaded Folding Blades for 100mm Ducting in Range Hoods and Bathrooms Fans, 4-Inch

This company puts out "quality" items Something we dont see to often anymore. This item works great when exhaust fan turns on and closes nicely when fan is off. I like the rubber gasket Keeps cold air from coming back into house BigBox stores carry similar item BUT not as well made and more money Highly recommend

I needed some sort of back draft prevention for my bathroom vent fan setup because I was getting bugs and draft in my basement bathroom. These fit right up to other 4 inch ducting, and I used rubber connectors to secure these on. They look sleek, work great, and they have a great quality seal and don't let air back in. They have a double flap to prevent back drafting. I used two of them in my set up to keep each line isolated before a combining y connection

Good

Eigentlich gut gemacht. Leider ist die Zentralachse, die die beiden Klappen führt, nicht 95mm lang, wie der Korpus der Rückschlagklappe, sondern 3-4 mm länger. Passt unter keinen Umständen in das Entlüftungsrohr. Nach eigenen Nachsrbeitungsversuchen dient es nun nur noch als Briefbeschwerer

Works great, well made metal. Slides right in place