|MadSci Network: Physics|
The secret is in the water. Water is a very good absorber of heat, and carries the heat of the flame away from the rubber skin of the balloon before it has a chance to raise it to its melting point. Native people used this same idea to boil water in skin bags, and it's still a popular bonfire trick to put a paper cup full of water on a fire and amaze everyone that it doesn't burn.
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