A guy here at work brought in a small sample of Aerogel, a material that is 99.8% air, incrediably light, works as an insulator, and is the lightest known manmade solid. It is designed for the space program to aid in the collection of space dust.
It’s so light and translucent it almost isn’t there, yet it is a solid! You can hold it in your hand and bounce it up and down and it makes a cool “clicking” noise when it comes down and hits your skin. Very neat stuff, but a bit expensive if you can find it. There are some ebay auctions for it though.
The guy said that it was one of those things you see and just can’t not buy, and it is pretty cool. No idea what a normal person would need with it though, other than to show others and have them go “coooooooool”.