What are the strongest dog toys? Charles Goodyear well known for his tyre empire created the first rubber tennis ball with felt stitched along the outside. This was developed as the rubber vulcanization process became popular in the 1870s. Not a lot has changed and dogs still love the fun that this simple toy delivers. With some improvements made to theses tennis balls - strength and of course a squeaker! You'll need a few of these balls around the house, in the car or in your doggy bag for those fun active games of fetch. Available in small and large.