Aluminum foam is neat stuff, made by melting the metal down and adding a bubbling agent while it's in liquid form. The resultant material looks like a sponge, is up to 95% air, is fireproof, sound-dampening, reflective, and can absorb a high amount of impact force. The military is incorporating aluminum foam in Humvees (click on "Blast Mitigation" at link) to absorb IED blasts, and Frank Gehry's making a building complex out of the stuff. The informative (but occasionally silly) nine-minute video below takes a closer look at the material and how it's made: