The 501 is considered the “No flip flop, Flip Flop”. Designed with the same contoured insole for arch support as the 301 with the addition of a wider strap holding the foot in place for more support and comfort. The upper is made with bullhide and backed in suede, stitched with double bonded nylon thread and a toe thong made of durable tubular nylon, suede insole and Vibram soles.