The Babolat Academy tub contains 72 "pressureless" balls which are suitable for use with a ball machine or training. These balls will never go flat, so they are very economical. Depending on the surface you use these on, you can get months or years out of these before eventually the felt will wear off the outside. The felt is extra durable to provide the maximum life possible.
Pressureless balls are a better option for ball machines because they all have the same bounce and feel which can allow you to achieve consistency from the shots fired.