What is the name of the foam used to back drive bay covers? I'm looking to get some white foam from somewhere as the hole diameter on the mesh is quite big and I think that foam will look good.
Don't beileve it's anything special, you should be able to find rolls of foam somewhere and then just simply cut to the appropriate size. Granted, if you're specifically looking for a certain foam that ships with certain cases then i'm unsure where any case maker gets there foam from.
Maybe contact them and see if they can point you in the right direction.
You ask, "...used to back drive bay covers". And then you talk about air passing through. I suspect what you are looking at is the sheet of dust filter that is mounted inside the front of the case, just in front of your HDD mounting bays.
Most such filters are made of polyurethane foam sheet, but a particular type. Polyurethane foam comes in two fundamental types - closed-cell and open-cell. In closed-cell foam, the tiny bubbles in the foam all are complete spheres, so there is no passage from one bubble to another, and these cannot allow air flow. This is used often in protective packaging applications where you do not want water to penetrate the foam. In open-cell foams, the bubbles are not complete, and there are air flow paths from one bubble to another, so these types are used for air filters, synthetic sponges, etc.
If you're trying to find something like that, check computer shops for sheets of air filter material.