Why do billiard balls turn yellow?
Most billiard balls are made of hard plastic materials that are resistant to cracking and chipping. As sometimes happens with plastics, over time exposure to UV light, combined with exposure to heat and oxygen, can cause a process called photodegradation through photooxidation. This breaks down the chemical structure of the plastic, creating disrupted plastic molecules that absorb UV light and re-emit it at a lower wavelength in the visible range, changing the perceived color of the plastic.
