calimaero® Seal Backdraft Shutter 4 Inch Inline Extractor Fan Backdraft Shutter Quiet Rubber Flaps, Fits All DN 100mm Ducting/Made from Recycled Plastic in DE

It does what it is supposed to, rare these days. Others have said it was too small, so either there was a duff batch previously or their pipe wasn't 100mm, (4 inches). The silicone membrane also laid mainly flat, but it is possible to gently smooth it out from where it is gripped by the central bar as you can see, it lies perfectly flat, it is not intended for insulation, just to stop the draughts, and be light enough to open when the fan is on. Mine fitted snuggly in a100mm pipe,the rubber fin gasket compressing to seal. Due to the poor original fitting of the pipe, I then discovered air going around it between the wall and pipe, coming into the room thru the fan casing. It is therefore worth sealing inside and out if accessible, to ensure no gap between pipe and brickwork, before condemnation of the product! My wall faces north across a field,and the shutter has stopped the wind rotating the fan in reverse, thus preventing a cold draught in the bathroom. It has proven silent in operating thus far.

Works well, nicely made and a good press fit into some horizontal 100mm plastic duct coupling. Only criticism is the price (paid £17).

Very easy to instasll and does the job. Seemed a bit flimsy when imfirst recieved it but in used it's perfect. Fits very snug in the 100mm opening of the extractor vent.

Would not recommend, the rubber seal is very thin and was sealing properly as it's very flimsy. Ended up throwing it straight in the bin

Fits easily into the trunking. ( Make sure it’s the right way round ).So far has cut that really annoying draft.

Product looked good. Outside rubber seal good. Like others I think the central bar needs to have a more permanent fix. Even when I was fixing into pipe it kept coming off. Flaps were a bit too flimsy also when I was fitting the wind was making them flap open. From the wrong side. Awkward to fit because of its flimsy construction. Yet to see if it reduces the air ingress. Very pricy product misleading a little. Lots of more sturdy products on the market. Shame as idea was very good. They just need to sort the design out better.

The product is fine and does what it is supposed to do (ie stop back draughts).However the information in the product description and packaging is very poor. This product will only work in a vertical flow up situation ie the air flow is up a vertical section of ducting. It will not work in a horizontal or flow down situation as it relies on gravity to shut the flaps.The product will fit and appears to seal in flexible 100mm diameter ducting. This is also not clear from the description.

So jury is out ATM as to whether this is doing the actual job it's supposed to. When it arrived I was disappointed with how flismy it seems - but it fits well and was easy to attach so now it's a wait and see if it lasts/does the job it needs to