I've seen case mods with large holes covered with, or entire case panels of modders mesh; however I do not feel comfortable with my hardware that exposed. Which leads to my question:

What kind of natural air flow could one expect through a large mesh opening with an a/c type foam filter?

In my experience filters like this do fine when a fan is sucking directly though them, but will air pass though without a fan, or just a fan in another part of the case?

Probably not well which is why foam is such a great insulator.

I'm not familiar with the foam you are referring to but you'd want the thinnest, most porous, open-cell foam you can find.

Modder's mesh, or perforated metal, comes in a variety of hole sizes and spacing. mcmaster.com has a really good selection followed by onlinemetals.com.

Take a look at Modright filters. Perhaps you can use them.

http://www.modright.com/cat/l1/g54/Fan_ ... d=TYD6ifob