Plastic pellets are used for cushioning stones in the rock tumbler. If you are tumbling things that are soft or brittle, you need to start cushioning from the very beginning of the tumbling process. If you are tumbling harder stones, the more common types such as jaspers, agates, petrified woods with a Mohs hardness of 6 to 7.5 - you dont need to cushion the stones until they start getting thin because thats when they chip as they bang into each other. Some people always cushion at the polish stage ... some people only cushion at the polish stage... some people cushion at the pre-polish and polish stages ..... if your stones are large enough you dont have to cushion them ..... every one of your tumbles will be different .... When using these pellets in the tumbler, please understand it is impossible to clean these pellets perfectly after using them. If you use them in a tumble with coarse grit you need to rinse them off, dry, and store in a bag marked with the grit size or polish you ran them with, and do NOT use them with any other size grit. Tiny particles of the original grit can be embedded in the plastic and if you use those pellets in a tumble using finer grit, the coarse could come out and contaminate your batch and scratch your stones. You can, however, use these pellets over and over and over again, just make sure you keep them separated. How to clean and save? Its easy. When you dump everything into a plastic bucket and start washing, the pellets will float to the top of the water. Just put in a sieve and rinse until clean, and then dry before you put them away.