Aerogel, also known as frozen smoke, is the world's lowest density solid, clocking in at 99 percent air.
Aerogel is a synthetic porous ultralight material derived from a gel, in which the liquid component for the gel has been replaced with a gas. The result is a solid with extremely low density and extremely low thermal conductivity. Nicknames include frozen smoke, solid smoke, solid air, solid cloud, blue smoke owing to its translucent nature, the way light scatters in the material. Silica aerogels feel like fragile expanded polystyrene to the touch, while some polymer-based aerogels feel like rigid foams. Aerogels can be made from a variety of chemical compounds.
Aerogel is a material that is 99.8% air. Aerogels have a porous solid network that contains air pockets, with the air pockets taking up the majority of space within the material. The dearth of solid material allows aerogel to be almost weightless.
Aerogel was first created by Samuel Stephens Kistler in 1931, as a result of a bet with Charles Learned over who could replace the liquid in "jellies" with gas without causing shrinkage. Aerogels are produced by extracting the liquid component of a gel through supercritical drying. This allows the liquid to be slowly dried off without causing the solid matrix in the gel to collapse from capillary action, as would happen with conventional evaporation.
The first aerogels were produced from silica gels. Kistler's later work involved aerogels based on alumina, chromium, tin dioxide. Carbon aerogels were first developed in the late 1980s. Aerogel is not a single material with a set chemical formula; instead, the term is used to group all materials with a certain geometric structure.