If Michelangelo's famous marble statue of David was made of aerogel, it would weigh only 4 pounds (2 kilograms)! Aerogel is one of the least dense substances on Earth, a foam-like solid material that holds its shape despite being almost as light as air. Some types have densities just three times heavier than air, but typically aerogels are 15 times heavier than air [source: Aerogel.org].
You might think of gel as a wet substance, such as hair gel. But aerogel is made by removing the liquid from a gel. All that's left is the silica structure — which is 90 to 99 percent air. Aerogel is almost weightless, but can be spun out into thin sheets of aerogel fabric. In construction projects, aerogel fabric demonstrates "super-insulating" properties. Its porous structure makes it difficult for heat to pass through. In tests, aerogel fabric had two to four times the insulating power of traditional fiberglass or foam insulation [source: LaMonica]. Once the price comes down, it could be widely used in construction.