This is the world's lightest material. Dandelion seeds. "I think it's the other thing." Oh, right. Some sort of hollow metallic lattice. How light is light? Try over 100x lighter than Styrofoam. WTF KIND OF SORCERY IS THIS?!
The material is a micro-lattice in structure, with the 0.01 percent of the material that's solid consisting of hollow tubes that are only 100 nanometers thick. It's rated at a density of 0.9 mg/cc, lighter than even the lightest aerogels, which have only achieved 1.1 mg/cc. It's also extraordinarily strong and shock-absorbent, thanks to all that air: it can compress by 50 percent and completely recover its shape, highly unusual for a material that is essentially metallic. It was actually inspired by architectural structures rather than other ultralight materials--the team looked to the Golden Gate Bridge and the Eiffel Tower to see how those structures are so light and yet so strong.
Man, I'm not sure lattices should compete in the same "world's lightest material" category as other, solid things. It already had an unfair advantage on account of being mostly empty space. And speaking of mostly empty space: my apartment. Help, I've been robbed.
Thanks to Emilio, Rev Dr Dom and ANTE, who tried filling a mattress with helium to make a hover bed with unimpressive results. It, uh -- it didn't work? *calls to cancel Helium tank*