Aerogel- the lowest density solid in the world (until March 2013).
While its name suggests it feels like gel, Aerogel feels like polystyrene to the touch, and is both solid and rigid.
Instead, it is named Aerogel because of its composition; this example is Silica aerogel which, as the name might suggest, is derived from silica gel- a granular, porous form of silicon dioxide. Silica aerogel (hence referred to as simply aerogel) is the most common form of aerogel, and is the most extensively used and studied.
The gentle blue colour of aerogel is thought to be cause by Rayleigh Scattering of short visible light wavelength- the same reason the sky is blue. The pores of aerogel are just under 100nm in size, and it is these pores that cause the gel to appear a smoky blue against dark backgrounds, but a yellow colour against a bright background; much like the sky.
Aerogel’s density is 1900 grams per cubic metre, while Air has a density of 1200 grams per cubic metre. This made it the lowest density solid until as lately as March 2013, until the discovery of aerographene, whose density is 160 grams per cubic metre. This low-density property of Aerogel makes it a perfect insulator. In 2011, Aerogel held as many as 15 Guinness World Records, including the world’s best insulator.
Pictured left is a demonstration of the amount of insulation that aerogel provides. A bunsen burner is burning below the aerogel, and a flower is placed upon it. The heat from the bunsen has no effect on the flower, due to the insulation provided by the remarkably low-density solid.
Since the creation of Aerogel, mountaineers have worn coats insulated with it. Aerogel is ideal for mountaineering- It’s light, thin, and insulates marvelously. However, it insulates a bit too well. Mountaineers have complained that they are too hot when climbing Mount Kilimanjaro, since their coat is providing too much insulation. Who would have thought people would ever complain about the heat several thousand feet in the sky?