Amazing!  World’s lightest metal which is 99.9 percent air can sit on top of a dandelion fluff without damaging it.  They used Abaqus extensively for the realistic simulation of the hollow based lattice structure.  You can compress the structure by 50% and bounce back to normal shape. Popular Mechanics awarded the worlds lightest metal top 10 innovators for 2012.

UCI mechanical & aerospace engineer Lorenzo Valdevit and fellow researchers at HRL Laboratories LLC, along with the California Institute of Technology, have won a 2012 Breakthrough Award from Popular Mechanics for their creation of a micro-lattice metal. The material is lightweight enough to sit atop a dandelion's fluffy seeds without damaging them (pictured) yet is also extremely strong. "I am really honored to be selected as one of the winners," Valdevit said. "The material we have developed is ultra-light and ultra-compressible, but more importantly, it's a unique platform for a novel methodology. This development has been the result of an extraordinary collaboration. I want to thank my colleagues and friends at HRL and Caltech for creating such an enjoyable research environment." The team was able to make a material that consists of 99.99 percent open volume by designing the 0.01 percent solid at the nanometer, micron and millimeter scales, using an innovative fabrication process.

Popular Mechanics award for world's lightest metal 

See Article Here:

The reference for the published conference proceeding paper is: 

S.W. Godfrey, L. Valdevit, ‘A novel modeling platform for characterization and optimal design of micro-architected materials’, 2012 AIAA Structural Dynamics and Materials Conference, Honolulu, HI, Apr 2012. AIAA Paper # 2012-2003