Zeus DUO chew toys are made of a unique duo of durable, non-toxic materials to provide your dog with a thoroughly enjoyable chewing experience. The rigid nylon center is covered by a soft yet resilient outer layer that your dog will just love sinking their teeth into! Great for playing fetch of solo chewing. High-quality Thermoplastic Rubber outer. Durable Nylon inner. Delicious mint scent. Tiny openings in the outer layer for the scent to pass through.