Aerogel is a manufactured material with the lowest bulk density of any known porous solid. It is derived from a gel in which the liquid component of the gel has been replaced with a gas. The result is an extremely low-density solid with several remarkable properties, most notably its effectiveness as a thermal insulator and its extremely low density. It is nicknamed frozen smoke, due to its translucent nature.
…! Don’t miss the photo of a 5 lb brick resting on a piece of aerogel weighing only 2 grams. It basically looks like it’s floating.