Airgel is an ultra-light porous synthetic material derived from a gel, in which the liquid component of the gel has been replaced with a gas, resulting in a solid with extremely low density and low thermal conductivity . Nicknames include “frozen smoke,” “solid smoke,” “solid air,” or “blue smoke” because of its translucent quality and the way light scatters through the material. However, it feels like Styrofoam to the touch. Aerogels are solid, rigid, dry materials that do not resemble a gel in their physical properties. Gently pressing on an airgel usually doesn't leave even a small mark; pressing more firmly will create a permanent depression. Although it is susceptible to shattering, it is structurally very strong. Aerogels are good thermal insulators because they are good at counteracting the three methods of heat transfer (convection, conduction and radiation). They are good conductive insulators because they are composed almost entirely of a gas, and gases are poor conductors of heat. Silica airgel is particularly good because silica is also a poor conductor of heat (a metallic airgel, on the other hand, would be less effective). Aerogels are poor radioactive insulators because infrared radiation passes directly through the silica airgel. Aerogels themselves are hydrophilic, but chemical treatment can make them hydrophobic. If they absorb moisture they usually undergo a structural change, such as shrinkage, and deteriorate, but this can be prevented by making them hydrophobic. Airgel was discovered in the late 1930s by chemist Samuel Stephens Kistler. It achieved this through the supercritical fluid drying process. A supercritical fluid is any substance at a temperature and pressure above its critical point… the center of the paper… the first spacecraft. Particles vaporize upon impact with solids and pass through gases, but can become trapped in aerogels. • NASA used airgel for thermal insulation of the Mars Rover and spacesuits. • The US Navy is evaluating airgel undergarments for use as thermal protection for divers. • Dunlop Sport uses airgel in some of its tennis, squash and badminton racquets. The production and use of silica airgel does not pose a danger to the environment. No significantly hazardous waste is generated during their construction. Disposal of silica aerogels is harmless. In the environment they quickly break down into a fine powder, essentially identical to sand. Furthermore, silica aerogels are completely non-toxic and non-flammable. If they eventually find widespread use, they could eliminate a large amount of unwanted and dangerous plastic materials.