Fan filters...are these fine enough?

Solution
Your best bet is to simply install a finer mesh filter and turn the fans down. The best mesh granularity is a function of the type of dust you're dealing with. If it's getting through the filters, you need something finer.
1mm is on the wider end.

I'd personally go for something in the 0.25 to 0.5 mm range with a (real) mesh construction. Those filters are made of a perforated sheet, which won't have as much open area to let flow through as an actual wire mesh.
 


Reason I was looking at the ones I linked to is because they are $8 for 10 filters as opposed to $6 for one. But I wanted to check to see if they were any good first which is sounds like they aren't. I have a filter panel on the front of my case that's a mesh fabric and does an ok job. I was thinking of adding a second filter to each front panel fan for more filtration as long as the air flow isn't too restricted. I was also thinking of adding another fan to the side panel to add more positive pressure to the case but there's no filter at all in that location so I need to add something there for sure if I do actually add a fan rather than just sealing off the vent.

Perhaps I'll try some HAVAC filter and hot glue and make a filter for the side and then figure out something for the front. Those filters are cheap enough and I might actually already have some that I can try and see how it works out.
 


First, two filters won't help much, especially if you already have a mesh type filter.

Second, side intakes aren't a particularly good idea for most people. They don't provide any benefit over a properly designed fan setup.

Third, HVAC filters are WAY too restrictive for use with computer fans. They're significantly higher restriction than the worst radiators.

What are you trying to accomplish with these changes, exactly?
 
Less dust. Even with the panel dust filter it's a short amount of time before the fans are caked in dust and of course the inside of the case is covered as well. Bad thing is...it's not like I live in a dirty house. We clean the floors regularly but it doesn't help having two kids and a dog. Daily dusting and sweeping of the floors barely seems to keep up with things.