system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do some plastics discolor and turn white when they are stressed/bent?
gpt
For plastic it actually creates micro fractures in the structure in a process called work hardening. The white is basically tiny air voids retracting light differently. There are no chemical changes to the structure it's just mechanically breaking down. If you were to measure the density of it at that point you would find it has decreased. 


It's similar to how you can beat egg whites into a foam.