Open Knee Support 708 by LP Support is a closed cell neoprene support, with an extra knee support to reinforce the patella and provide stability, which in turn helps against displacement of the knee cap... Keeping the patella free from coverage relieves pressure and helps to keep as much freedom of movement as possible... The closed cell neoprene retains body heat which in turn increased blood circulation to aid healing and give relief to weak or injured knees... Measure around mid-section of the knee while in a standing position. 29.2-32.7cm-XS... 33-35.6cm-S... 35.9-38.1cm-M... 38.4-43.2cm-L... 43.5-50.8cm-XL...