What is fire made of, fire molecules? I used think it was heat so hot you could see it but, "NO". It's not matter it's not a form of matter either. It is a visible energy, like sunlight. Fire is caused by something called combustion.Combustion happens if well, say you have a fire, you have to start it with combustion:
Fuel,
Heat,
&
oxygen.
These elements create the chemical reaction as I said before called combustion.