This human-made material is known as the world's best heat insulator. Aerogel has been used by NASA, amongst others. 96 % of the structure consists of nothing but air. The material has a seethrough appearance, but it is extremely strong and can hold up to 2.000 times its weight without collapsing!
Aerogel is created by drying a gel via supercritical drying, which removes liquid slowly to maintain the structural shape.