Aerogels are engineered compounds which are 99.8% air, and are known as the lightest solid known to man. The most common type is a silica based compound which is molecularly very close to glass. They have a texture similar to that of styrfoam, and florist green foam, but if they are placed under enough direct pressure, such as squeezing it to hard it will shatter like glass. NASA is currently researching them for their insulation properties, while also imploying them to catch "stardust" particles.