These INSUM dog balls for medium or small dog tennis balls are made of natural rubber and felt, which are more dog-friendly and non-toxic, making them a great toy ball for dogs to chew, chase and grab.. This dog tennis ball comes in a variety of bright and eye-catching colors, which can be easily found and recycled when playing outdoors, and will not be confused with other tennis balls at home. This tennis ball can be played at home, on the lawn, in the park, or even in the swimming pool.