I just now came across this thread and...Oh noes! My shoddy craftsmanship on one of my first foam replacements has come to light, I see. Sorry about those flowers, just_add_coffee.
Yeah, it's not very special looking material, and it really isn't. It's simple shelf / drawer liner, but it works pretty well and you can add as many layers as you like in different places if there are certain parts of the board that are looser than others, ie. the F122.
The other day when I was in Harbor Freight I noticed that they have black or grey toolshelf liner of two different thicknesses. The thinner of the two looked like it might make a nice foam to try, but I was in a rush and didn't get any. Maybe something to check out if you're looking for easily available materials, though I suppose not everywhere has a HF store nearby either.
Btw, in case you are wondering what those red things are on the space bar stabilizer wire, they are anti-rattle covers that I got from stripping some small gauge wire and using just the sheath. I really don't like rattle, so I do stuff like this as well as adding a small amount of Kapton tape to larger wire stabs like on the shift, enter, or backspace, depending on the keyboard.