Stirrup strap: captures heel to restrict ankle motion. Stabilizing straps: form figure-eight to protect and support ankle. Dynamic cuff: protects against high ankle sprains. Low profile: will fit in any type shoe. Bilateral design: each size fits left or right foot. Ballistic nylon boot: provides tremendous strength and durability. Velcro lace closure: easy application. US manufacturing: higher quality control standards. Measure ankle circumference around the heel: XS (10-11"), S (11-12"), M (12-13"), L (13-14"), XL (14-15"), and XXL (15-16").