This easy-to-use device is designed to keep tension on the tissue (plantar fascia) so it heals in a stretched position at night. When worn as prescribed, it does not allow the plantar fascia to contract while in the prone or supine position. The device holds the ankle and forefoot joints in a position of slight dorsiflexion prevents a position of plantarflexion, thus the plantar fascia is not allowed to contract. In addition the involuntary stretching of the plantar fascia over a long period of time helps to strengthen the foot's arch. Fits left or right. Measure the calf at the widest point. Latex free.