25mL of the world's lightest known solid material. Also commonly called "frozen smoke". Safe to touch, but it may leave a sticky residue.
Aerogels are a group of materials in which the liquid portion of a gel has been replaced with a gas. It was first created as a result of a bet.
Being the lightest solid material know, aerogels are up to 99.8% air. Its also has the lowest thermal conductivity of any know solid.
Due to their high porosity, NASA has even used aerogel to collect interstellar dust particles in outer space.