i have some fiberglass mesh(about 1mm gaps in the threading) which i have over the 80mm intake in my case, and it's horrendously dusty down here in the basement, it does a decent job of keeping the dust out, and i just need to run my hand over it once to get all of the dust up
of course, the inside still gets dusty, but it's not a concern of mine. so long as it doesn't catch on fire, i'm ok