Aerogel
Aerogel is a silicon-based substance often called frozen smoke or blue smoke. It is composed of 99.8% air and is a stiff foam with a density of 3 mg per cm3, which makes it the world's lowest-density solid.
This substance has many interesting properties including a highly dendritic structure, extremely low thermal conductivity, which gives it remarkable insulative properties, a melting point of 1,200 °C.
There are a variety of tasks for which aerogel is used. One use is by NASA for trapping dust particles, as it did aboard the Stardust spacecraft.
Aerogel was created as a result of coordinated research between NASA and Aspen Systems, Inc.. It is made by drying a gel composed of colloidal silica in an extreme environment. Specifically, scientists start with a liquid alcohol like ethanol and mix it with silicon dioxide to form a gel. Then, through a process called supercritical drying, the alcohol is forced out of the gel, typically with high-pressure carbon dioxide. With this drying process, the gel does not collapse or lose its volume. It appears bluish because the silicon dioxide scatters shorter wavelengths of light much like air in the daytime sky. Despite its diaphanous appearance, it feels like hard plastic foam.
Aerogel holds 15 entries in the Guinness Book of Records for material properties, including best insulator and lowest-density solid. Aerogel can support 2000 times its own weight without collapsing.
