How Is the Rubber Inside a Baseball Made?

According to the rules of Major League Baseball, section 1.09 states: "The ball shall be a sphere formed by yarn wound around a small core of cork, rubber or similar material, covered with two stripes of white horsehide or cowhide, tightly stitched together." The rubber within a baseball is usually synthetic and similar to that used to make pencil erasers and tires.

  1. Natural vs. Synthetic Rubber

    • Natural rubber is derived from a latex contained in the sap of certain plants. It is technically an elastomer, or a hydrocarbon polymer with elastic properties. When natural rubber is purified, it becomes the chemical polyisoprene, which can be produced synthetically to make synthetic rubber. There are several patented varieties of synthetic rubber, including Hypalon, Neoprene, Viton, Kaltrez and Silastic.

    Creating Synthetic Rubber

    • Soon after the discovery of rubber in the 1700s, scientists worked out how to create the substance artificially. Chemists took samples of natural rubber and heated them to break the material down, which resulted in tar, oil and isoprene. The chemists correctly reasoned they could combine small amounts of isoprene made from oil to create synthetic rubber. In a strange twist, modern-day synthetic rubber comes from the same substance that powers our cars.

    Inside the Baseball

    • Synthetic rubber has many uses, and sometimes it gets made into a small ball measuring in at 13/16th of an inch. These small spheres are used by baseball manufacturers as the core of their product. After being enveloped by a black layer of synthetic rubber, followed by a red layer of synthetic rubber, the completed ball is called a pill. The circumference of a baseball pill is 4 and 1/8 inches.

    Other Uses of Synthetic Rubber

    • In addition to its use inside baseballs, rubber is manufactured into a wide range of products. While the primary uses for the material are tubes and tires, rubber is also used for belts, window profiles, gloves, balloons, matting, gaskets, dampeners, rubber bands, flooring treatments and pencil erasers. Rubber is also produced in long strands, or fibers, called elastic.

    The Cork Alternative

    • Baseball manufacturers also have the option of using cork cores instead of rubber cores. Cork comes from the bark of the cork oak, which can only be harvested once every nine years per tree. Cork oaks are not sufficiently large enough for bark harvesting until they are at least 25 years old. A careful combination of soil care and tree pruning are required to produce this lightweight, fibrous material.