This 10 lb. Power Systems Power Grip Bag appears to be made with a heavy duty neoprene fabric that is soft and flexible. If I had to guess, which is exactly what I am doing, it is filled with a fine-grain sand or similar substance. I believe this would have many uses whether in the gym, at home, or on-the-go.
If you have any questions, please feel free to email as I am happy to help.