Rubber cores were made from melted shoes, wrapped in yarn and leather.

1840s, players crafted homemade hardballs by wrapping small objects; rocks, walnuts and even fish eyes. They would wrap these with yarn before stitching a piece of leather around the orbs.

National Association of Base Ball Players adopted rules in 1858 that required baseballs to have rubber cores covered with yarn and leather. Weight, size and rubber percentage however, were not governed allowing home teams to tailor them to the strengths of their teams.

1901 to 1910 Major League Baseball used a Rubber Core Baseball.

Rubber remained the primary core of the baseball until 1910 when the A.J. Reach & Company began production of a ball with a center of cork encased in a layer of vulcanized rubber that was patented the year before by Ben Shibe, owner of the Philadelphia Athletics.

This was the beginning of the Dead Ball era (1901-1919). During the fall classic of 1910 a baseball with a center cork was introduced.

During the fall classic of 1910 a baseball with a center cork was introduced. The American and National Leagues both adopted the cork-centered ball in 1911.

Cushioned Cork

Introduction of a Cushioned Cork Center.

The National League and American League agreed to standardized the baseball. A cushion cork center; two wrappings of yarn; a special rubber cement coating; two more wrappings of yarn; and a horsehide cover.

Natural rubber shell with less-elastic balata center core.

Japanese cut off rubber supplies at the onset of World War II. Four days after the 1941 bombing of Pearl Harbor, the United States banned the use of crude rubber in any items deemed non-essential to the war effort—including baseballs. The 1943 season was forced to replace the core’s natural rubber shell with less-elastic balata, the same substance used to make the hard outer shell of golf balls.

Spalding introduced the Synthetic rubber core.

Wartime restriction were uplifted and crude rubber returned to baseballs once again.