The 20 Pound Burly Medicine Ball is used primarily as a strength tool for low volume slower speed movements.All balls are 14 inch in diameter impact absorbing and moisture resistant. The casing is sewn from 18 oz. flexible vinyl coated polyester. The standard colors are black and gray but many custom color designs are available. The casing design and construction insures that the implement remains dimensionally stable and balanced. The Dynamax trade secret and craftsmanship utilize the casing to retain the various fibrous cores under tension so that each ball regardless of weight has the friendly feel and will absorb high velocity impact. Each ball carries a warranty against stitch and lacing failure.