There is no difference between ‘flammable’ and ‘inflammable’; inflammable is not the opposite of ‘flammable’ as some people think. When you say that something is ‘flammable’ or ‘inflammable’, what you mean is that it is something that can easily catch fire.
Example: I understand that the chemicals stored in the factory are highly flammable/inflammable.
When you say that something is non flammable, what you mean is that it is something which doesn’t catch fire easily. Another word which has more or less the same meaning is ‘non inflammable’. One might say that these two words are the opposite of flammable and inflammable.
Example: If you are planning to walk through fire, wear this. I understand it is non flammable.
Source: “The Hindu” – Know Your English Column – Jan 22, 2008