It really depends on the ball. Two-piece balls have a solid rubber core (heated and pressed into shape) and an exterior covering of thermoplastic (ionomer resin). More exprnsive three-piece balls have either a solid rubber or liquid core with rubber wire wrapped around it to keep it under tension. this keeps the ball hard and stops it from losing its shape. This is given a coating of ionomer, balata rubber or polybutadiene, a special plastic based on petroleum that provides bounce. The latter, however, must be mixed with zinc to strengthen it. Three-piece golf balls can take 80 manufacturing steps, 32 inspections and 30 days to make one ball, whilst two-piece balls take half the steps and can be made in a day.