Many pool balls are made of phenolic resin, a material that is heated until it becomes hardened, while others are made from polymer or polyester. Phenolic resin pool balls are designed to absorb the impact of a pool cue hitting the ball.
Phenolic resin balls are capable of withstanding 50 times the impact of other balls. Plastic and polyester balls are an improvement over past ball materials, such as celluloid, which often caused balls to explode on impact. For a time, pool balls were made from ivory, which required the slaughter of elephants. Many of the earliest pool balls were made from wood.