Plastic replaced celluloid in most new table tennis balls from 2014.
The change followed safety and practical concerns surrounding celluloid, a highly flammable material that had been used for table tennis balls for more than a century. The International Table Tennis Federation approved non-celluloid balls as the sport moved toward a new equipment standard.
Early plastic balls were often called “poly balls,” although manufacturers have used different plastic compounds. Players noticed differences in sound, bounce and spin, so the transition produced considerable discussion among professionals and coaches.
Celluloid balls did not disappear instantly. During the transition, both celluloid and plastic balls appeared in competition and training. Modern approved balls remain hollow, spherical and 40 millimetres in diameter, but their material is generally plastic rather than celluloid.