The world's lightest (and errie looking) solid
Looking like the ghost of a real solid, Aerogel is 99.8% air and 1,000 times less dense than glass but is rough enough to survive a space launch's high temperatures and provides 39 times better insulation than fiberglass. As cool as this so-light-it's-almost-not-a-solid solid is, it's hard to believe it was invented in the 1930s. Nasa recently used it on their mars pathfinder to collect cometary samples and interstellar particles aboard the Stardust mission.
Although much less dense than glass, Aerogel is another silicon-based solid but is composed of individual features only a few nanometers in size linked in a highly porous structure. Its unusual properties include low thermal conductivity, refractive index and sound speed - but it's the ability to slow down and capture fast moving dust with minimal heating or other effects that would cause their physical alteration that grabbed NASA's attention.