Aerogel is the world's lowest density solid (96% air). It's a gel made from silicon, except all the liquid has been replaced with gas. If you hold a small piece in your hand, it's practically impossible to either see or feel, but poke it, it's like styrofoam. Aerogel supports up to 4,000 times it's own weight and can withstand a blast from two pounds of dynamite. It's also the best insulator in existence, which is why we don't use it in clothing, people would overheat.