iPower 4 inch Shutter Back Draft Blocker, One-Way Airflow Ducting Insert Backflow Preventer with 2 Inline Springs Loaded Folding Blades, 4" Backdraft Damper, for HVAC Extractor Fan Vent, Range Hoods

This backdraft is excellent, fits well into the 4" stove pipe system, and is functioning quietly. I would buy again.

I live in a humid area. So to prevent my bathrooms from getting humid, I simply went into the attic, cut the 4" flexible duct coming from the bathroom exhaust fan going to the soffit, and inserted one of these between the two cut ends of duct. (is a ONE way shutter so just be sure oriented in proper direction)Did this for four ducts. Worked perfectly.

I bought this unit and a significantly more expensive competing unit. This one is sturdier by far and it has 2 springs on the flapper vs 1 on the other.The big issue is that neither of them are accurately made so to get a good flapper seal there is a very wide foam gasket the flapper seals against. It seals well but this is a small duct to begin with and I calculate that the big gasket reduces flow area by a whopping 57%! This is a pretty big flaw but I only deducted 1 star because for my situation my fans move too much air anyway. If airflow is too restricted the flapper shaft on this unit is easily removed and I can easily trim back or replace with a more reasonable gasket.

The draft stopper works. It has a rubber gasket it bumps against so is fairly air tight. It also keeps out rodents because it is a 1-way flap. This was one of the better prices I found

This duct is not 4" to fit inside snuggly into a 4" pipe. Like others have stated many other issues with this beside the size. Poor quality, poor design, poor manufacturing.

Our bathroom vent blew it's baffle off twice and I am tired of fishing it out, lol. This worked and fit perfectly! It's very quite and makes no noise. It's built sturdy and was easy to install.

Mine arrived with one of the two spring closing doors unable to open due to the door hitting the spot weld. I had to take it apart and peen it with a hammer. Not high quality control. You get what you pay for......

First one I got sent was a little rough, and the foam was off and sticking, this time around it turned out to be good well put together item, does it’s purpose very well!!