The Nerf Dog Balls have been designed for small dogs and puppies and will keep them entertained for hours on end. 2 of the balls are made of tough thermoplastic rubber, this toy will stand up to extensive chew sessions. And, they float! The other 2 balls are tough tennis balls. All of the balls are great for toss and catch sessions and also solo play sessions. All 4 balls are suitable to go in the Nerf Dog Tennis Ball Blaster for Small Dogs and Puppies.