Plastic pellets act as a cushioning media when tumbling delicate materials such as obsidian, cabochons, etc. The price listed for the small, oval shaped plastic pellets, (food grade, floatable, polypropylene), is for one pound and they will fill a plastic bag approximately 5" x 8".
When tumbling and using plastic pellets, pour the material from the tumbler into a bucket of water. The pellets will float to the top for easy removal with a strainer, and then rinse them and reuse many times. For more tips on tumbling with plastic pellets see the tumbling article: Tumbling with rotary or barrel tumblers.
Other uses for the plastic pellets: stuffing for dolls, bean bags, etc.