Aerogels

What looks like blue smoke and feels like styrofoam?

Well...aerogels, obviously...

So these are pretty cool, actually.  Aerogels are the least dense of all solids (natural or otherwise).  Wikipedia - my faithful friend - tells me that they are made by replacing the liquid in a gel with a gas.  Seems logical.  Tricky to do though...evaporation has to occur really, really slowly so that the whole thing doesn't collapse like my mom's puff pastries (sorry, Mom).

Anyway, they are quite strong (though they shatter easily), they are great insulators (all that air), and they can leech all the water out of your hands if you hold onto them for too long (darned desiccants). 

Go ahead and do a quick Google Image search of these things - they're quite sci-fi and pretty.  You may think you've never come into contact with them...but you just might be wrong.  Apparently they've been used in paints and cosmetics, for insulating skylights and windows, and as a delivery system for certain drugs.  And yes, also in the space exploration, nuclear technologies, and environmental cleanup industries...but that's another story.