Aerogel holds 15 entries in the Guinness Book of Records, more than any other material. Sometimes called “frozen smoke”, aerogel is made by the supercritical drying of liquid gels of alumina, chromia, tin oxide, or carbon. It’s 99.8% empty space, which makes it look semi-transparent. Aerogel is a fantastic insulator — if you had a shield of aerogel, you could easily defend yourself from a flamethrower. It stops cold, it stops heat. You could build a warm dome on the Moon. Aerogels have unbelievable surface area in their internal fractal structures — cubes of aerogel just an inch on a side may have an internal surface area equivalent to a football field. Despite its low density, aerogel has been looked into as a component of military armor because of its insulating properties.