When a rubber band is stretched, the polymer chains that make up the rubber are pulled apart. This causes the entropy of the system to increase, which in turn makes the rubber band more elastic. However, as the rubber band is stretched further, the polymer chains become more aligned and the entropy of the system decreases. This makes the rubber band less elastic and eventually causes it to break.

The point at which the rubber band breaks is called the breaking point. The breaking point is determined by the strength of the polymer chains and the amount of force that is applied to the rubber band.