UPDATED (19/11/2011): There is a lighter material than aerogel! It is named “ultralight metallic microlattice”, currently flaunted as the lightest material on Earth! View the full news article here: Click!
Aerogel is a synthetic porous material derived from a gel, in which the liquid component of the gel has been replaced with a gas. The result is a solid with extremely low density and thermal conductivity. Aerogels are almost completely composed by gas!
Properties of Aerogel:
- Extremely low densities (can be made lighter than air!)
- Excellent heat insulation properties
- Prone to shattering
- Hydrophilic (generally)
Note: There are many types of aerogel. e.g. silica, carbon, alumina, etc.
Pictures from aerogel.org
You can learn how to make Aerogel here + its a great site for information on Aerogel: http://www.aerogel.org/
You can buy Aerogel here to play with or just be fascinated by it: http://www.buyaerogel.com/
Book on Aerogel (For the interested): Aerogels Handbook (Advances in Sol-Gel Derived Materials and Technologies)
I found a video on the production of aerogel at home: