Balls have a rating system that uses stars that is determined by the manufacturer. Ranging from one to three, the best balls and the only balls you should use for most purposes are the three stars. These can typically be purchased in packs of 3, 6 or 12 or in bulk. Good quality balls last a long time when given the proper treatment. As of July 1, 2014, all ITTF events started using Plastic Polystyrene 'Poly' balls. The playing characteristics of the new balls are unique but very similar to celluloid. They transport more safely and are more environmentally friendly. Non-poly balls (celluloid) may still be legal for some tournaments and it is up to national and regional table tennis governing bodies to determine what type of ball to use for their tournaments. As of 2017 manufacturers started using a new type of plastic - ABS (Acrylonitrile butadiene styrene) - for table tennis balls. ABS offers improved roundness and durability over poly balls and is more environmentally friendly.