There is always a bit of dust on your filament spool and I had problems with thunderbugs which invaded into my monitor and my filament spool.
I wanted to prevent them from entering my extruder and influence the print result or block the heater.
So I decided to print a small case for a sponge. It doesn't need any support and prints at a layer height of 0.3mm within 20 minutes.
On Prusa i3 Hephestos it stands fine on the extruder. Might fit on many other printers as there is no special mounting required.
Feel free to modify this design. I attached the OpenSCAD design file as well as a rendered STL.
Doesn't need to be precise, so you can print in a layer height of 0.3mm. After printing, cut 15mm x 15mm blocks out of a sponge. I used a sponge with a height of 8mm, so I put two layers of this into the box. Make a hole into both sponges and put the filament through.