This got me excited.. A few days ago I read on boingboing.net that a website in the states is selling small pieces of aerogel, or liquid smoke, a substance developed by NASA that is 99.8 per cent air. Small bits about the size of a quarter are going for $30 USD plus shipping.. or you can get larger ones for $125. Unfortunately, they only ship within the US.
A few aerogel facts:
It can hold over 2000 times its weight.
Typical density: 3 mg/cm3
Melting point: 1,200 °C (2,192 °F)
Used on NASA's Stardust mission to gather samples from a comet.