|MadSci Network: Chemistry|
Most of the hot fluids I can think of boil well below the temperature at which paper or polystyrene would burst into flame. There is a famous book by Ray Bradbury, "Fahrenheit 451", which is supposed to be (I have never checked) the temperature at which paper burns, while water boils at 212 °F. I suspect that if your fluid was a high-temperature silicone oil heated to a high enough temperature, or molten lead, you would see some convincing flames when you tried to fill your cup. There are several answers in the archives which will give you more info about styrfoam, if you search with that word. In particular the temperature of melting point. Thanks for the question.
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