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Windings Inside a Baseball

When unraveling a baseball, what you’re likely observing are indeed both in the form of long strings, but they serve different purposes and come from different stages in the baseball’s construction.

Wool (as a material within baseballs), when referring to wool in the context of baseballs, it usually pertains to wool yarn or wool fibers that have been spun into yarn. Wool, due to its resilience and cushioning properties, is often used in near the core of the baseball to help the ball maintain its shape and provide a certain level of elasticity when hit.

Yarn is a generic term for a continuous length of interlocked fibers. In the manufacturing of baseballs, several types of yarn can be used, including wool yarn, cotton yarn, or synthetic yarn, depending on the desired qualities of the baseball. Each type of yarn can serve a different purpose, such as contributing to the weight, durability, and compression of the ball.


So, when you’re unraveling a baseball and finding long strings, you’re essentially looking at different types of yarn. Some of this yarn might be made of wool, chosen for the characteristics wool lends to the ball, such as elasticity and the ability to return to shape. Other yarns might be made from different materials, used for their strength, durability, or other desired properties in the construction of the baseball.

Types of Materials

Wool is a costly fiber to produce and process (PDF), leading to the utilization of various sources to meet the demands of baseball manufacturing. Wool fibers are typically crimped and have a scaly surface that allows them to interlock and create a warm, durable fabric. The quality of wool can vary based on factors like the length, thickness, and crimp of the fibers.

  • Cashmere: This is a luxury fiber obtained from the underbelly hair of the Cashmere goat. It is known for its incredible softness, lightness, and insulating properties.
  • Alpaca: The fiber from the Alpaca is similar to wool, but is often softer, lighter, and more durable. It is a popular choice for high-end garments.
  • Mohair: Harvested from the Angora goat, mohair is a lustrous, strong, and resilient fiber that is often blended with wool.
  • Angora: The soft, downy fur from the Angora rabbit is exceptionally warm and lightweight, making it a premium natural fiber.
  • Silk: While not a protein fiber like wool, silk has a similar smooth, lustrous feel and is often used in high-end clothing and textiles.
  • Merino Wool: This is a particularly fine and soft variety of wool that is highly regarded for its comfort and thermoregulating properties.

In addition to natural wool yarn, there are synthetic materials that are comparable to wool in terms of their properties and applications:

  • Acrylic: This synthetic fiber is designed to mimic the look and feel of wool, while often being more affordable and easier to maintain.
  • Polyester: Another synthetic option, polyester provides many of the same performance characteristics as wool, such as wrinkle resistance and durability.

Industry Standards

Wool grading is complex and can be based on several factors, including fiber diameter, length, color, crimp, and purity. While the textile industry does not adhere to a singular, universal grading system for wool yarn, it employs a variety of methods focused on fiber characteristics that influence the yarn’s quality and suitability for different uses. Other than generic wool grades mentioned below, baseball manufacturers do not disclose any specific wool yarn grades for their baseballs.

Wool Grades

The differences among these materials used for winding layers can be attributed to their color, quality, origin, and treatment, which can all affect the performance and quality of the final baseball product. Let’s break down the distinctions:

  • White Virgin Wool Winding: Virgin wool is often stronger and more resilient because it hasn’t been weakened by previous processing. White virgin wool yarn is commonly found in the fourth winding (finishing) layer in professional-grade baseballs.
  • “Finest Grade” Grey Wool Winding: The term “finest grade” often refers to the wool fiber’s diameter (fineness), length, and strength. Grey wool is a natural color that can come from blending white and black sheep wool or from sheep that naturally grow grey wool. The high quality of this wool makes it ideal for contributing to the durability and performance of the baseball, most often used in the first or second winding layer that require high resilience and strength.
  • Grey English Wool Winding: Grey English Wool specifies wool that is sourced from England, known for its quality wool products. The term “grey” again refers to the natural or blended color of the wool. English wool can vary in quality, but it generally has a reputation for being durable and of high standard due to the country’s long-standing wool production practices.
  • Grey Wool Winding: This is a more general category that describes wool windings without specifying origin or grade. The color is grey, which, like the others, could be due to natural color or a blend. The lack of descriptors such as “finest grade” or “virgin” suggests it may not meet the same quality standards as the more specifically named types. This material is used in innermost layers where high-quality standards are less critical than in the outer layers but still contribute to the overall performance of the baseball.


For baseballs, an array of yarns, including woolen varieties, are intricately layered and wound tightly to create the ball’s inner framework, which is subsequently encased in leather.

In the production of professional-grade baseballs, the winding assembly features four distinct layers of wool and poly/cotton yarns. Each layer wraps around the cushioned cork core in concentric circles, with each layer distinguished by its unique thickness.

  • Layer 1: consists of four-ply gray woolen yarn, representing the most substantial thickness. When tightly wound around the core, this layer extends the diameter of the nascent ball to 7-3/4 inches (19.68 centimeters).
  • Layer 2: a layer of three-ply wool yarn is applied, expanding the diameter to 8-3/16 inches (20.77 centimeters).
  • Layer 3: also a three-ply gray wool yarn, further augments the diameter to 8-3/4 inches (22.22 centimeters).
  • Layer 4: The final layer employs white poly/cotton yarn, designed as a finishing touch, culminating in a total diameter of 9 inches (22.85 centimeters), thereby completing the winding process.

In Closing

Material selection for baseball manufacturing is critically influenced by age-appropriateness, desired properties, cost, and the nuanced differences in wool quality, origin, and treatment. For professional-grade baseballs, the choice of durable, high-quality wool or wool-blend yarn is essential for optimal structure, strength, and performance, considering each type of wool—from virgin white to the finest grade English grey—provides unique attributes that enhance the ball’s construction and performance during play.

In contrast, for younger players or more budget-conscious options, manufacturers may opt for synthetic or recycled acrylic or polyester yarn, balancing cost with functionality.

This approach to material choice underscores the important role of the winding material in determining the baseball’s final characteristics and its ability to withstand the challenges of the game.

To read more about baseballs, please visit my reference page Buying Baseballs – Reference Articles. If you found this post to be helpful, please do me a favor and sign up for my newsletter.