i bought these after missing a landing off a pipe and doing some nerve damage to my knee. they fit like a neoprene knee support you can by from the any sports store. i've had no problems with slips. i was surprised with how well they work; much better than simple foam pads. you need to figure out how to get them to fit best based on the shape of your legs and how they bend, but once you have the dialed in the work very well.