Its called microlattice. Material was developed by scientists at UC Irvine and Caltech. It is lighter than styrofoam and as shown in the picture above can sit atop a dandelion without crushing it. From Popular Science:

The key structural component is a series of hollow tubes. In a study published last November in Science, the researchers exposed a light sensitive liquid to UV light through a patterned mask, which created a three-dimensional photopolymer lattice. They then deposited a layer of nickel-phosphorous onto the polymer lattice, which was then etched. The remaining structure was a macroscopic material with hollow tubes as the base structural elements. The resulting material had a density of .9 mg/cm³. By comparison, ultralight silica aerogels are 1 mg/cm³.

Though metallic microlattice is the lightest metal developed to date, it held the title of lightest material for less than a year. Aerographite, a carbon material developed by researchers at the Technical University of Hamburg and University of Kiel (and first reported in an Advanced Materials article in June 2012), weighs in at just .2 mg/cm³.