Instead of buying the Giant Solar Baloon, which is 50 feet long, to demonstrate how hot air expands and rises, we used a very light weight black plastic garbage bag. We filled the bag with air, tied a string to it and just let it lie in the sun while we did other experiments.
A solar balloon is a balloon that gains buoyancy when the air inside is heated by the sun's radiation. The balloon is made of very lightweight black material, since dark colors absorb heat more effectively. The heated air inside the solar balloon expands and has lower density than the surrounding air, causing it to float.