Knitting balls, also known as YARN balls, are a type of spool used to store and dispense YARN for knitting and crocheting. They are usually made of plastic or wood and have a hole in the center to allow the YARN to be pulled through. The YARN is wound around the ball in a circular pattern, allowing it to be easily accessed when needed. YARN is the most common material used for knitting balls, but other materials such as cotton, wool, and synthetic fibers can also be used.