system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does tempered glass work? How does it stop the actual screen from cracking?
gpt
The idea of tempered glass is that they make it so that the surface of the glass is squeezed hard - it is under compression. To balance this, the inside of the glass is being pulled apart, or 'under tension'

This means that it takes a lot of force to break the surface of the glass, because that would involve pulling it apart, but you can't pull it apart, because it is being pushed together.

They do this generally in one of two ways - either they cool the glass down quickly, so the outside sets before the inside cools and contracts; or they use chemistry to stuff big atoms into the glass. These big atoms take up more space, pushing on their neighbours, squashing them and making that compression.