Eggcrate?, the foam stuff or the plastic grid cover for lighting? Sorry to sound like a dolt
No, egg crate is what is commonly called 'light defuser'. It is cheap stuff that is used commercially to cover up fluorescent lights in buildings. Basically plastic squares. I have it under my sand bed, as a cover for my tank, and made frag racks out of it. Pretty useful stuff if you look at it. The sizes of the holes are JUST right.
Bingo. Sniper beat me to it. Handy stuff indeed.