Also known as frozen smoke, Aerogel is the world's lowest density solid, clocking in at 96% air. It is basically just a gel made from silicon, except all the liquid has been taken out and replaced with gas instead. If you hold a small piece in your hand, it is practically impossible to either see or feel, but if you poke it, it is like styrofoam.
Aerogel is also quite useful. It supports up to 4,000 times its own weight and can apparently withstand a direct blast from two pounds of dynamite. It is also the best insulator in existence, which is why we do not have Aerogel jackets: it works so well that people were complaining about overheating on Mount Everest.
