Aerogel

http://commons.wikimedia.org/wiki/File:Aerogelbrick.jpg

Yup, that’s a brick.

It’s sitting on Aerogel, “frozen smoke,” the world’s lowest-density solid. The stuff is 99.8% air but can support 2,000 times its own weight, and it holds 15 entries in the Guinness Book of Records.

Most amazingly, it was first created in 1931.