The problem is in the stride. With flat feet the inside edge of the foot and the big toe stay slightly off the ground, causing an ineffective push-off. So feet must roll inward (over-pronate) to be entirely on the ground before becoming an effective lever to push. Flat Foot Insoles, developed by orthopedic surgeon Dr. Michael Pryce, compensate for the biomechanical problems and pain associated with flat feet. Molded from polyurethane with a shock-absorbing Poron socklining, Flat Foot Insoles support the inside edge of the foot and big toe as if they were in contact with the ground throughout the stride. Feet stay in alignment - offering relief from ankle, knee, hip, and back pain. Please specify Men's/Women's shoe size. Cannot mix sizes for quantity discount.