Breakthrough material is barely more than air

Researchers at HRL Laboratories, the California Institute of Technology, and the University of California at Irvine have created what they say is the lowest-density material, a lattice of hollow tubes of the metal nickel.
Its volume is 99.99 percent air, and its density is 0.9 milligram per cubic centimeter–not including the air in or between its tubes. That density is less than one-thousandth that of water.