Here're two different ways of doing it, I'd label them egg-crate and monobloc. I'm not sure which method the claim is made for. Corrugated sheets laminated into a block is immensely strong.
In either case. it's the air that does it, allowing room for the paper fibers to crush under sufficient force. If you see a modern plastic bumper with the cover off, there is a plastic egg-crate inside.
order99 -- Don't forget the cup-holders! Also, this:
