https://www.youtube.com/watch?v=7i6pUgEGLZI
I never imagined ping pong balls were so extremely flammable but, as this video shows, only a few of them can cause a giant tower of fire several feet high.
According to the YouTube found by Redditor ShlawsonSays,they are so flammable because they are celluloid, which burns really fast. And it seems that old ping pong balls—made of acidified celluloid—were even worse. They would become unstable over time and heat from friction would set them on fire.
