Natural rubber moulded into a 4" pinecone, and the shape is doing real work — the ridges give it an unpredictable bounce, so a backyard throw doesn't just roll to a stop. The grooves between them massage the gums while the dog chews, and they hold a spread-on treat if you want to stretch the session out. Flexible enough not to punish teeth, built for medium to large dogs, and it goes in the dishwasher.