Simple, versatile, and fun to use, the Firm Core Stability Ball is designed to challenge your balance, stability and flexibility through various low-impact exercises and movements. Included with the package is a 30-minute core training video that guides you through a variety of techniques that you can adapt to your training, stretching, rehabilitation or other workout routines. The ball is made of tough, burst-resistant plastic, a special material that resists tearing and, if punctured, deflates safely and gradually. Available in several fashionable colors, the 55-centimeter ball is sized for users measuring between 5 feet and 5 feet, 5 inches.