I wonder how they keep the chips so fresh and crisp inside those plastic bags?

Nitrogen And Nitrogen

Yes, nitrogen. Did you ever notice how a potato chip bag feels a little bit inflated? It's almost like a little balloon.

Potato chip bags are not full of air, but of nitrogen gas. This is done to prevent the chips from oxidizing, which is part of what makes them go stale. Oxygen is very reactive, and likes to combine with other molecules whenever it can, causing chemical changes to take place. Nitrogen, however, is very stable and unreactive. A so-called "nitrogen atmosphere" is good for storing foods that oxidize quickly, like potato chips and bacon.

Although many people think air is the same thing as oxygen, about seventy-eight percent of the air we breathe is actually nitrogen gas. Nitrogen is all around us.

Read More:

"Science in a Bag of Potato Chips." EducationWorld.com.