system
Given the following post, respond as if you're commenting on Reddit:
human
When paper dries after being wet, why does it dry wrinkled instead of drying flat?
gpt
The paper expands to some degree when hydrated. When drying, different parts of the paper dry at slightly different rates due to slight differences in the surrounding area and the slight randomness with which water evaporates. As it finishes drying, these variations become fixed.