Flammable vs. Inflammable – What’s the Difference?

If you are stuck in the wilderness with nothing to help you survive except a box of matches, you will want to know which things you can use to build a fire.

Some things burn easily, and some things do not. Flammable and inflammable are adjectives that say basically the same thing.

But which is which? If you are really trapped in the wilderness, fighting for your own survival, adjectives might be the last thing on your mind. But if you are writing, especially in the context of physics, you will need to know the difference between these words.

What is the Difference Between Flammable and Inflammable?

In this article, I will compare inflammable vs. flammable. I will use each of these words in several example sentences to give you an idea how they appear in context.

Then, I will tell you a mnemonic device that will allow you to choose inflammable or flammable correctly every time.

When to Use Flammable

define inflammable define flammable What does flammable mean? Flammable is an adjective. If something is flammable, it can be set on fire.

Technically speaking, almost anything is flammable if it can be brought to a high enough temperature. Under normal circumstances, however, things like paper, gasoline, and dry wood are flammable, while things like steel, granite, and water are not.

For example,

  • The factory received a safety citation for storing flammable chemicals too close to the welding booth.
  • The contents or aerosol cans can be extremely flammable, and it is best to keep them away from sources of heat.
  • The rules for the ethanol fleet were part a broader set of regulations issued Friday to make all tank cars that haul flammable liquids sturdier. –The Wall Street Journal

Flammable is related to the Latin verb flammare, which means to set on fire. Other words, the noun flame, the adjective enflamed, and the participle flaming all have similar origins in Latin.

Flammable was first recorded in English in 1813.

When to Use Inflammable

what is flammable and inflammableWhat does inflammable mean? Inflammable is also an adjective, and it has the same meaning as flammable, which causes understandable confusion.

One might think that the prefix –in has the effect of negating flammable, thereby describing something that is resistant to flames. This, however, is not the case.

While most –in prefixes have negative meanings, the ­–in used in inflammable is formed using a different Latin prefix –in, and it has the effect of intensifying the word. In other words, inflammable is something that is easily set on fire.

  • “Too Much Johnson,” which had been shot on highly inflammable nitrate stock, had apparently been lost to the ages. –The New York Times

Inflammable was the standard word to describe something that is flammable for hundreds of years. The standard negative term was noninflammable.

In recent years, however, flammable has gained some traction.

flammable versus inflammable

definition of inflammable definition of flammable definition

As you can see from the above charts, which chart flammable vs. inflammable over time, flammable, and it’s correlative nonflammable, has clearly gained traction and might be eclipsing inflammable.

Ultimately, this is a positive change because it creates less ambiguity. Many readers upon seeing the word inflammable think that the subject is resistant to flames. Words like flammable and nonflammable eliminate this possibility for confusion.

Trick to Remember the Difference

Since both of these words mean the same thing, you really don’t need a trick to remember their difference.

  • Both flammable and inflammable mean easily set on fire.

While the have the same meanings, flammable is the better word choice because it eliminates the possibility of confusion in the reader’s mind.

A good way to remember to use flammable over inflammable is that it is a simpler word, as is it’s opposite.

  • Flammable = able to be set on fire.
  • Nonflammable = not able to be set on fire.


Is it flammable or nonflammable? Flammable and inflammable are both adjectives that mean easy to set on fire.

  • Flammable is the standard term in the 21st century. Nonflammable is its opposite.
  • Inflammable is a term that is best avoided because it creates ambiguity. Noninflammable is its opposite.