These terms are ones that are often confused simply because they do not mean what you think they should mean.
Flammable means that something is capable of being ignited, easily burned.
Inflammable means the same thing.
Non-flammable means incapable of being ignited, not easily burned.
So why the confusion? Well, the prefix “in-“ in English means “not” and is closely related to the similar prefixes “un-” and “im-.” That is how we arrive at such words like unfair, inexplicable, impossible, and so on. However, in this case, the “in-“ prefix is not the English “in-“ prefix. It’s Latin. In Latin, adding the prefix “in-“ to a word was a way of intensifying the term. We see this used in the words enflame, engulf, intense, and so on. The problem is that most people confuse the two prefixes and think that inflammable means that something cannot be ignited or burned. Not true.
How does this affect you?
Well, it probably doesn’t in your normal life. However, most usage experts agree that the term inflammable should be avoided since most people confuse the correct meaning. After all, you’d hate to make that mistake when you really needed to get it right. For the sake of understanding, use flammable and non-flammable.