Podiatrists and orthopedic specialists use this product more than any other to comfortably protect the back of the heel, and the lower portion of the Achilles Tendon from pressure and friction. It is the only product which protects these areas without slipping. It is composed of a comfortable elastic sleeve, with a long lasting gel cushion designed to absorb pressure and friction, rather than allowing these forces to "work" on the skin and soft tissue. The gel cushion is thin enough to fit in any shoe, yet it is durable and will provide you with comfort for many months. The entire guard is washable, including the gel cushion. Size is determined by the circumference of your ankle. This is measured with a tape measure placed around the ankle.