My kids, and all their friends, love to create foil art at my house.
You can purchase a box of 500 sheets for about $7 at Sam's.
The rules are simple. You may only create your art with the foil sheets and nothing else. No pipe cleaners, markers, tape etc. This really forces them to think about how to mold the foil into the shape that they want.
Here Hannah shows off her princess crown and foil butterfly.
This art project can keep them busy for hours when it's just to hot to play outside.