"World's 'lightest material' unveiled by US engineers" – BBC

Dezeen Wire:
a team of engineers based in California have created a material made from a lattice of hollow metallic tubes that they claim is the lightest in the world – BBC

The substance is 100 times lighter than Styrofoam and consists of 99.99% air. Tubes with a wall thickness 1,000 times thinner than a human hair are used to create the lattice structure that gives the material it's strength. Potential applications include shock and sound absorption and thermal insulation.