Here is the intro he wrote to his project.
"One day my dad found a flat ping pong ball and by just trying to fix it he gave me the idea that started this. He said that you could use boiling water to make the ping pong ball re-inflate. He was right. It did work and I wanted to investigate further and learn why the hot water made the ping pong ball round. With my parents’ help, I researched and found out about the Montgolfiers’ technique. By making air inside of an object hot, the air expands and the object will expand. I wondered which kind of heat would work the best to re-inflate a ping pong ball. I decided to test two different types of heating methods, 5 times each. I used boiling water as the first heat source and a hair dryer for the second heat source."
Here are the county winners for each grade level. I thought it interesting that all the elementary winners were male and the upper grade winners were female.