system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do storage containers keep cookies crisp when they have air inside them?

How do containers like Tupperware stop cookies and crackers going soft since there's still air inside the containers with the food?
gpt
They go soft because they are absorbing moisture from the air. When out in the open, there's an infinite (for all intents and purposes) amount of moisture for them to absorb, but when closed in a container, they can only absorb the moisture in the small amount of air in the container with them. At some point, the moisture level in the air reaches an equilibrium with the cookies/crackers and they don't absorb any more. The same thing happens with things that go stale, like bread, but in the opposite direction. They want to dry out, but when in a closed container the air inside can only hold so much moisture. The rest is forced to stay in the bread so it stays soft.