For a pull-on neoprene sleeve, fit determines most of the comfort and function. Measure the circumference of your knee at the centre of the kneecap with your leg straight and muscles relaxed. Compare that number with the measurement guide printed on the packaging, not with your usual trouser or sock size. If the measurement falls between two sizes, follow the guidance provided by the manufacturer on the package; when in doubt, it is safer to choose the option that does not press into the tissues.
The 510-2 is 23 cm high, so it covers a section above and below the knee. When worn, the sleeve should sit evenly around the joint, with the opening edges lying flat and the fabric not folding or bunching behind the knee. The compression should be noticeable but comfortable: enough to create a steady sensation during bending and walking, but never enough to cause pain, throbbing, numbness, tingling, or bluish discolouration. If you see deep red lines that remain long after removing the sleeve, the fit is too tight.
Try bending the knee a few times right after putting the sleeve on. It should stay in place during shallow squats, walking, and normal leg movement without sliding down or rolling at the edges. If it does slide, re-check the measurement and the size guide. A sleeve that is too loose will not provide the mild compression and heat retention described for this product, while an overly tight one can create discomfort. If you have had recent injury, surgery, marked swelling, or ongoing pain, it is wise to speak with a clinician before selecting and using this support.