Holding a piece of aerogel is an uncanny experience. It's so light it feels nearly weightless, like a chunk of solidified fog or smoke. It feels a bit like Styrofoam, and it squeaks when you rub your finger on it. It's strong enough to support many times its own weight if the load is distributed evenly. But bend it or squeeze it too hard, as one Wired News editor discovered, and a chunk of aerogel will shatter into tiny fragments.
The Bad Astronomer (Phil Plait) also remarked on how light it is.
At 3 milligrams/cc, aerogel is pretty thin stuff; water is over 300 times denser. A cubic meter of aerogel would only weigh 3 kilograms, less than, for example, my cat. A cubic meter of water weighs a ton, by the way.
He called it solid smoke. :)
Extremely kewl stuff.
Wired News: A Solid That's Light As Air