The new and improved Avoli V.2 Knee Pad.  

Now with a stay-in-place cuff and multi foam construction.
Made with a tight-weave, ballistic-grade material that repels moisture. 

The V2 kneepads come with their own carrying case.  The case has back loops that allow you to clip it onto your bag, an adjustable closure and mesh ventilation to speed drying.

How to find your size: Using a measuring tape, measure the circumference of your thigh just above the knee while keeping your knee slightly bent.