[Art]

...that is the World's Lightest (or actually least dense) Solid?
Comprised of 99.8 % air, great thermal properties and practically transparent to name a few...

Meet, Aerogel.

https://www.youtube.com/watch?v=AeJ9q45PfD0

[Freddy]

Fascinating - I was hoping he would squish it or something so we could get an idea of the texture.

[Art]

He did try squeezing it and it crumbled. It's more of a solid than a squishy piece of foamy air-filled plastic, I should imagine.
Very cool none-the-less.

[HS]

Maybe it would be a bit like charcoal. But even lighter and more brittle.

[Art]

And almost transparent and heat resistant and non-flammable and extremely lightweight and...
charcoal?

[HS]

Well... apart from all that. 
I donno they just seem similar to me. Like the porosity, the brittle texture, it seems like they would sound similar when dropped onto a table.

[8pla.net]

Invented 88 years ago, now interplanetary.