Training table tennis balls are a handy and applicable to many situations. They are effectively used in multi-ball practice drills, beginner’s play and robot training. It makes a lot of sense and is always cheaper to buy training balls in bulk. Training balls are perfect for a insert into a ball trainer but we also carry larger diameter 44 and 55 milimeter balls to slow down the game for beginers play. Generally speaking training balls are less durable and break easier. You wouldn't use them for regular play as they are very thin. However, when you want to train a lot, these are perfect. Great price!