Can Metal Be Lighter Than Air?
Yes. Well almost.
That is, if you arrange the atoms just so. "The world's lightest metal contains hardly any metal at all—in fact, it is made up of 99.99% air. Called a microlattice, the material is a three-dimensional grid of tiny tubes that is up to 100 times as light as Styrofoam (1)." The tube walls are 1000 times thinner than a human hair (2). (The microlattice is compared to the structure of human bone.)
"In addition to its ultra-low density, the material's cellular architecture gives rise to unprecedented mechanical behavior for a metal, including complete recovery from compression exceeding 50% strain and extraordinarily high energy absorption." "Boeing says an egg wrapped in the new material would survive a 25 story drop (2)."
The Boeing Company wants to build airplanes with it, as the material is as strong as aluminum but half the weight; and lighter weight translates into reduced fuel use. NASA, who is paying for the research, hopes to use the material for flying to Mars (1).
Sources: (1) Time Magazine. Nov. 2, 2015. P. 25. In the near term, you can see the photograph by finding this issue in the student lounge. It's in the issue with the Fusion illustration on the cover.
(2) Daily Mail. http://www.dailymail.co.uk/sciencetech/article-3270060/The-end-heavy-metal-Boeing-shows-material-99-99-AIR-lead-new-generation-planes-spaceships.html#ixzz3r1gv8AM8.Accessed Nov. 9, 20015. Also shows the photograph, a portion of the material resting on a dandelion seed head.