For just $250 on eBay, you could pick up a big chunk of Aerogel, also known as the world’s lightest solid. Put simply, it’s “a low-density solid-state material derived from gel in which the liquid component of the gel has been replaced with gas.” Auction page. Video after the break.
Aerogels are produced by extracting the liquid component of a gel through supercritical drying. This allows the liquid to be slowly drawn off without causing the solid matrix in the gel to collapse from capillary action, as would happen with conventional evaporation.