BOLT’s Dura-Grip Slam Balls are made of thick, reinforced rubber and designed for high-impact throwing exercises. The Dura-Grip’s exterior is designed with square slip-resistant ridges, and the inside is filled with sand to enhance the ball’s weight, balance, and firmness. The list of exercises you can do with a slam ball is extensive, and the benefits extend far beyond muscle growth. Studies show that plyometric exercises improve injury recovery, general athleticism, and muscular tone. BOLT’s Dura-Grip Slam Balls are versatile full-body exercise tools and a great addition to any gym. Get them in five varieties, ranging from 10 to 60 pounds.