Where to find small pieces of foam

[MasonJar]

I second (third?) the suggestion of the scrap or cut bin at Home Depot Lowes, or other. Also take a look in the stacks of insulation in the aisle. Often there are someone that are damaged enough to be junk for their original purpose. I once got two sheets of 2" 2x8 for $5. They had broken corners, but I didn't care.

You might also try any nearby construction site. Lots of useful material in dumpsters, but ask before you dive!

Andrew