Softballs are comprised of two parts, including a core and a covering. The material used for covering is composed of synthetic, composite or natural leather, which is commonly dyed yellow to help with visibility. The leather is stitched around the ball with red thread made of either linen or cotton. While the covering of a softball remains consistent, its core can be comprised of a variety of materials.
The material used for the center of a softball’s core varies depending on the quality of the ball. Higher-quality softballs, like ones used for collegiate and professional play, have cores that are composed of long fiber kapok, a fiber obtained from a tropical tree in Central and South America, or polyurethane. These materials help to improve resiliency and durability of the ball, increase ball flight distance when hit, prevent bat damage and limit bat vibration and sting. In balls used for recreational and youth play, typically granulated cork, rubber, or a combination of both cork and rubber is used at the ball’s core. These materials are softer to limit injury potential in less-skilled players. No matter the material used at the core’s center, kapok, a fibrous yarn, is wound tightly around the center of the core to ensure that every ball is of the exact 12-inch size specifications.