system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: There is air in a bag of chips. So why do the chips only get stale after the bag has been opened?
gpt
The chips bags have an inert gas in them so they do not become stale, usually some sort of nitrogen gas.  When they are exposed the normal air, the oxygen and water vapor in the air starts to do their work.