Here's why:

* Polymers are long chains of repeating molecules. Rubber is made from a polymer called polyisoprene.

* Polyisoprene is a natural polymer found in the sap of rubber trees. It's a chain of repeating isoprene molecules.

* Synthetic rubbers are also polymers, often made by modifying or mimicking the structure of natural rubber.

So, whether it's a natural rubber ball or a synthetic one, it's fundamentally a polymer!