What Is a Baseball Made Of? A Complete Breakdown
A baseball looks simple, but its construction is more involved than most people realize. The core is cork and rubber, wrapped in layers of wool and cotton yarn, and covered by two pieces of cowhide stitched together with red thread. The final product must meet strict size and weight standards set by Major League Baseball.
The Core: Cork, Rubber, and the “Pill”
The center of a regulation baseball is called the “pill.” This small sphere is the foundation of the ball’s weight and bounce. In modern professional baseballs, the pill is made of a cork core encased in two layers of rubber — one black, one red. The cork is sourced from cork oak trees, and the rubber layers are vulcanized to create a firm, resilient center.
The pill is roughly the size of a large marble, about 1.5 inches in diameter. Its density is carefully controlled. A pill that is too heavy or too light will throw off the ball’s overall weight, which must be between 5 and 5.25 ounces according to MLB rules.
The Yarn Winding: Layers That Give the Ball Its Feel
Around the pill, the ball is wrapped in several layers of yarn. This winding process is what gives a baseball its characteristic weight and a slightly soft feel when squeezed. The yarn is wound under tension by machine, and the layers serve different purposes.
The first layer is a thick, coarse wool yarn that provides the bulk of the ball’s weight and helps absorb shock. The second is a finer wool yarn that smooths out the surface. The third layer is a blend of wool and synthetic fibers, and the fourth is a thin, tightly wound cotton or polyester yarn that creates a smooth base for the leather cover.
Each ball uses about 150 yards of wool yarn and 100 yards of cotton or polyester yarn. If the yarn is wound too loosely, the ball will be soft and lose its shape. Too tight, and the ball becomes too hard and heavy.
The Cover: Cowhide and Stitching
The outer cover of a baseball is made from cowhide leather. For many decades, horsehide was the standard material, but since the 1970s, Major League Baseball has used cowhide almost exclusively. The leather comes from the top layer of the hide, which is strong and flexible.
The leather is cut into two figure-eight shaped pieces, dyed a light tan color, and stamped with the MLB logo. The cover is glued to the yarn-wrapped core before stitching begins.
Each ball has 108 double stitches, meaning the thread goes through the leather twice for each stitch. The thread is waxed cotton or polyester, dyed red for high visibility. The stitches create friction between the ball and the air, which allows pitchers to throw curveballs, sliders, and other breaking pitches.
How Baseballs Are Made Today
Rawlings has been the official supplier of baseballs to Major League Baseball since 1977. The balls are manufactured in Costa Rica. The process is mostly manual, with workers winding the yarn, gluing the covers, and stitching each ball by hand. Each ball is inspected for weight, circumference (9 to 9.25 inches), and seam height. Balls that fail inspection are discarded.
How the Materials Affect Performance
The materials inside a baseball directly influence how it behaves during a game. The cork and rubber core determines the ball’s coefficient of restitution (COR), which is a measure of how much energy the ball retains after impact. A higher COR means the ball bounces off the bat faster and travels farther. MLB tests the COR of its baseballs to ensure consistency.
The yarn layers also affect performance. Wool yarn compresses slightly when the ball hits the bat, which absorbs some of the impact energy. This compression is what gives a baseball its “give” and prevents it from feeling like a rock. The outer cotton or polyester layer keeps the yarn from shifting inside the cover, which helps the ball stay round over the course of a game.
The Role of Humidity and Storage
Baseball materials are sensitive to moisture. The cork core and wool yarn can absorb water vapor from the air. A ball that has absorbed too much moisture becomes heavier and less bouncy. This is why MLB stores baseballs in a climate-controlled environment called a humidor.
The humidor keeps the balls at a consistent humidity level, usually around 50 percent. This practice started with the Colorado Rockies in 2002, because the dry air in Denver made baseballs harder and more likely to leave the ballpark. MLB now requires all 30 teams to store game balls in a humidor.
Key Takeaways
- A baseball has a cork and rubber core, wrapped in four layers of wool and synthetic yarn, and covered with cowhide leather.
- The red stitching is waxed cotton or polyester, and the 108 double stitches create the drag needed for breaking pitches.
- Rawlings manufactures MLB baseballs in Costa Rica, and each ball is hand-stitched and inspected for weight and size.
- Regulation baseballs weigh between 5 and 5.25 ounces and measure 9 to 9.25 inches in circumference.
