Next, there are balls known as practice or training balls. However, unless they are white or orange 40mm diameter balls weighing 2.7g, they will not be legal and cannot be used in competitive play. They can vary from very soft to very hard, and can usually be bought in packs of all one size or in mixed packs. These are available in lots of different colours and sizes and are particularly suitable for children and for fun, recreational play. There are many different types available and each one will be suitable for a different purpose. The new plastic balls are also known as "Poly" balls. Therefore celluloid balls have the inscription "40" or "40mm" whilst non-celluloid balls have the inscription "40+". One of the contentious issues about the new plastic ball was that it could potentially be slightly larger (up to 0.5mm) than the 40mm celluloid balls. However, the ITTF also said in 2012 that celluloid balls will continue to be "legal" for all other events for at least two more years, and possibly longer.
So in 2012 the ITTF agreed that, with effect from 1 July 2014, all ITTF events would only use table tennis balls made from plastic. The raw materials are considered hazardous to health and many countries no longer allow manufacturers to use them, so the ITTF was hoping that by changing to balls made of plastic, that they would avoid any future shortage of balls (due to shortages of the raw materials required to make celluloid balls). The ITTF said that the primary issue was with the manufacturing process used to make celluloid balls. This was a major change and one which caused a great deal of anxiety in the lower ranks of the sport. In 2011 the ITTF decided to promote plastic balls rather than celluloid balls.