From an LA Times article a year ago:

Scientists have invented a new material that is so lightweight it can sit atop a fluffy dandelion without crushing the little fuzzy seeds.

It's so lightweight, styrofoam is 100 times heavier.

It is so lightweight, in fact, that the research team consisting of scientists at UC Irvine, HRL Laboratories and Caltech say in the peer-reviewed Nov. 18 issue of Science that it is the lightest material on Earth, and no one has asked them to run a correction yet.

The material has been dubbed "ultralight metallic microlattice," and according to a news release sent out by UC Irvine, it consists of 99.99% air thanks to its "microlattice" cellular architecture.

"The trick is to fabricate a lattice of interconnected hollow tubes with a wall thickness 1,000 times thinner than a human hair," lead author Tobias Shandler of HRL said in the release.