Polyvinyl chloride (PVC) is produced by polymerization of the vinyl chloride monomer. Polyvinyl chloride is the world's third-most widely produced synthetic polymer of plastic (after polyethylene and polypropylene). About 40 million tons of PVC are produced each year. PVC comes in two basic forms: rigid and flexible. The rigid form of PVC is used in construction for pipe and in profile applications such as doors and windows. It is also used in making plastic bottles, non-food packaging, food-covering sheets and plastic cards. It can be made softer and more flexible by the addition of plasticizers, the most widely used being phthalates.