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Engineers Create World's Lightest Material
ackthpt writes "A team of engineers claims to have created the world's lightest material. Made from a lattice of hollow metallic tubes, the material is less dense than aerogels and metallic foams, yet retains strength due to the small size of the lattice structure (abstract). The material's density is 0.9 milligrams per cubic centimeter. Among other things, it's potentially useful for insulation, battery electrodes, and sound dampening."
on Cnet it specifically states that the .9mg/cm^3 is without air.
http://news.cnet.com/8301-30685_3-57327382-264/breakthrough-material-is-barely-more-than-air/?part=rss&subj=crave&tag=title
I normally don't link videos, but in this case it makes sense.
I think this is what he is talking about.
http://www.youtube.com/watch?v=HoCAxS4vqwQ
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Well, no: the material itself if still made of metal, and the metal has a density greater than atmosphere, and the atmosphere pervades through it (it's an open cell lattice). In order for it to float in air, you would need to enclose it (i.e., put a skin around it) and remove the air from the interior volume. The material needs to displace the air. The same could be said for boats: they float on water only when the hull has the water removed. Once the water gets inside the hull, you face the fact that the boat is made of metal and will sink. The buoyancy in air or water is based on displacing the fluid by something of lesser density. For a floating boat, replacing water with air. For a chunk of this foam, replacing air with helium, vacuum, etc.