Once the athlete tosses the ball to feel the weight, rolls it around to study the seams, and waits for the perfect pitch to hit, he will be transfixed by the power of the THUNDER HEAT® Polycore Softball. Technologically advanced for a superior play, this is the ball for your slowpitch game. 12 USSSA Slowpitch Softball Classic M Stamp Center: Poly Precision blended cross-linked polyurethane system High density and maximum resiliency Leather cover provides improved grip and protection Seams: Flat.