I love slam balls. I use it daily as a supplement to my workout. the ball is filled with sand and if it underinflated, the ball will lose its round shape, when it is slammed to the floor. just pump in some air to avoid this. this ball seems durable with a good grip. it is aerobic and a strength builder. it is a functional exercise to lift the ball from the floor to overhead and then slam it down to the floor. I love doing it.