Ultralight materials are very light substances. They include silica aerogels, carbon nanotube aerogels, metallic foams, polymeric foams, and metallic microlattices. The density of air is about 1.275 mg/cm3, which means that the air in the pores greatly lowers the density of the material.
The lightest material ever made was invented in 2011. It is made out of a microscopic micro-lattice of hollow tubes – a criss-cross diagonal pattern with open spaces between the tubes. The researchers say the material is 100 times lighter than Styrofoam and is very strong. The material is low density: it has a density of 0.9 milligrams per cubic centimetre. Silica aerogels, the world's lightest solid materials, are only as low as 1.0 mg per cubic cm. The metallic micro-lattices are 99.99% air and only 0.01% solid. The metal used is nickel.
- "The trick is to fabricate [make] a lattice of interconnected hollow tubes with a wall thickness of 100 nanometers, 1,000 times thinner than a human hair", said Tobias Schaedler.
The material is not just light: it has some elastic properties. When it is squashed, the little tubes are also squashed, but when the pressure is removed, they rebound. A sample squashed to half its height rebounds 98% when the pressure is lifted. That makes the material similar in some ways to elastomers: they are materials used to cushion against shock.
- Less than 10 mg/cm3
- Schaedler T.A. et al. 2011. "Ultralight metallic microlattices". Science 334 (6058): 962–965. doi:10.1126/science.1211649.
- World's 'lightest material' unveiled by US engineers. BBC Technology News: 
- Breakthrough material barely denser than air: CBS News Tech
- rebound = return to original shape