X-large Fits Knee Circum. 15.5 - 16.25 (measurement Taken Just Under The Knee Cap While Knee Is Slightly Bent) Thermal Support For Prevention Treatment & Rehabilitation Of The Knee Provides Protection And Support Against General Wear And Tear Including Sprains Strains And Twisted Knees Anatomically Shaped In 3 Pieces For More Comfort And A Better Fit Thermoskin Increases Elasticity Of Muscles Tendons And Ligaments To Reduce The Risk Of Injury When Under Stress And Strain Clinically Proven To Increase Surface Skin And Subcutaneous Temperature Between 2-3 Degrees F The Optimal Level To Make Tendons And Muscles More Pliable And Elastic To Provide Optimal Muscle Function