Heavy canvas and liberal use of leather and rivets for reinforcement around a steel hoop make up the basic design developed by Ivan Carper. MTDC modified the design in several ways (Figure 1). Overall dimensions were kept the same as the original, but 16-ounce (455-gram) coated nylon Cordura™ was used instead of canvas. MTDC did not use leather or rivets, but relied instead on sewn seams, which are stronger. MTDC also used tubular nylon instead of manila rope for the release cord. The bags were rigged with short chains and a snap clip to fit a decker saddle. With minor modifications, the bags could be rigged for a sawbuck packsaddle.
Partners in the testing and work project, the Professional Wilderness Outfitters Association, also fabricated some gravel bags using the basic Carper design. Theirs featured “truck tarp” fabric instead of canvas, manila release ropes, and rivets instead of sewn seams (Figure 2).