After a few years one of my ceiling extractor fans wasn't working well, and I found that the fan and ducting had become clogged with fibres drawn in through the vent. It was hard work to remove and clean the fan and replace the ducting, so I decided to put a simple filter behind the ceiling vent to reduce the need for maintenance. For a filter, I used a couple of cable ties and some mesh similar to that used to package fruit (in this case the mesh packaging of a new duct section). The photo below shows the "press fit" filter in place in the frame of the ceiling duct - some fibres have been caught after a period of use.
Of course it's important to ensure that the "filter" cannot impact the fan blades - here the tension of the cable ties holds the mesh in place at the start of a 1 metre long duct. I made a second filter, shown in comparison with the partially clogged one in the photo below.