The camouflage style pre-filled Hyperwear SandBell sandbag training free weight is so versatile it can be used like a medicine ball, slam ball, dumbbell or kettle bell. Soft, safe camo SandBells can also be thrown, caught and slammed allowing a vast variety of exercises individually or with a partner. Water resistant and the perfect weight for outdoor training and boot camps. Active, shifting movement of the sand challenges stabilizing muscles in your core giving you more results in less time. The ideal tool for grip strength endurance training. This model comes pre-filled with sand. US Patent 8,622,877 B2. SandBell is a registered trademark.