Evil Mad Scientist‘s blog has an interesting post on how egg crate foam is manufactured. Cool video!
Ever wonder how they make foam rubber into an “egg crate” shape? You can tell that it isn’t molded that way, because there is not a smooth skin on the surfaces. And it clearly isn’t milled to that shape, since it comes in matched top and bottom pieces that are cut from the same initial block of foam. So how is it done? Amazingly enough, it’s done with a bandsaw.
Egg crate, acoustic, and other shapes of “convoluted foam” are cut with a special machine called a convolutor, which uses powerful rollers to feed flat sheets of foam rubber into a high-tension bandsaw. The rollers are covered with bumps that stretch and distort the foam such that the saw cuts to a variable depth, with extremely little waste.
You can watch the process in this video from Italian Cutting Systems (noting that the bandsaws are hidden behind protective covers).