An exercise device includes an inflatable bladder and is partially stabilized with a small amount of filler. The bladder includes a first aperture to allow the filler to be easily placed in the bladder. The bladder also includes a valve main body that allows air to be easily injected into the bladder to inflate the bladder. In an exemplary method the filler is forced into the inflatable bladder using a mixture of air and filler. The air is under pressure and assists in forcing the filler into the bladder. After a proper amount of filler is in the bladder, the bladder can be deflated for packaging and/or shipping.