MT500 Hard Shell Knee Pads
"This padding is attached to a sleeve that extends quite high above the knee. An elasticated band at the top, furnished with silicone gripper, helps hold it in place. This is backed up by a broad Velcro strap.
A second strap just above the broadest part of your calf muscle lets you tailor the fit further, and there’s more silicone at the bottom.
All this means that, despite these not being the lightest pads out there, I had no issues with them slipping down or with material bunching behind the knee. They’re incredibly comfy too, even on lengthy rides with a lot of pedalling."