But aerogel is made by removing the liquid from a gel.
You might think of gel as a wet substance, such as hair gel. Some types have densities just three times heavier than air, but typically aerogels are 15 times heavier than air.
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. Engineers are even experimenting with nanoscale sensors that can monitor stresses inside building materials and identify potential fractures or cracks before they occur. Carbon nanotubes are so light and strong that they can be embedded into other building materials like metals, concrete, wood and glass to add density and tensile strength. These carbon nanotubes have the highest strength-to-weight ratio of any material on Earth and can be stretched a million times longer than their thickness. When a larger particle is divided into increasingly smaller parts, the proportion of its surface area to its mass increases. To construct materials at the "nano" scale would seem impossible, but using cutting-edge techniques like electron-beam lithography, scientists and engineers have successfully created tubes of carbon with walls that are only 1 nanometer thick. Even a strand of your DNA is 2.5 nanometers wide. Your fingernail grows approximately 1 nanometer every second. A single sheet of paper is 100,000 nanometers.
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