Though aerogel is technically a foam, it can take many different shapes and forms. The majority of aerogel is composed of silica, but carbon, iron oxide, organic polymers, semiconductor nanostructures, gold and copper can also form aerogel. However, within the aerogel structure, very little is solid material, with up to 99.8% of the structure consisting of nothing but air. This unique composition gives aerogel an almost ghostly appearance; hence it is often referred to as ‘frozen smoke