Making knee inserts - Neoprene? EVA? Polymers?

I'm going to be making some of my own knee inserts for my paintball pants, along with some openable pockets out of canvas or heavy gauge cotton. The main reason I'm opting to make my own knee inserts instead of buying commercially available knee guards or inserts is simply because of area coverage; while the ready made pads/inserts look good, I want something that covers a much bigger area on/around my knee/upper shin (about 15-20cm wide x 20cm high....thereabouts). Ideally, I would like to be using either

or sheets, but I can't find where to buy d3o in sheets, and sorbothane sheets are ridiculously expensive. From doing a fair bit of research and legwork, what I'm probably going to use is some EVA closed cell foam (perhaps 20mm thick), and perhaps some really tough and flexible neoprene (perhaps 2-5mm thick), then glue these two sheets together. I'd have the tough neoprene on the outside to protect against rocks and boulders, and the soft(er) EVA foam closest to my knee for cushioning. I've got a reasonable idea about the various materials, but I was hoping to get some advice from someone that may have tried this already. In particular, specific advice regarding materials and (metric, not imperial) densities (e.g. EVA of density x, and/or neoprene of density y, or perhaps different materials). Just saying "go use some dense foam" isn't going to help me at all. Obviously the thinner the inserts are, the better....but I want to adequately cushion and protect my knees/upper shins. I was also thinking that if I was to make these pockets on the outside of my pants, I could possibly get away with making the inserts a bit thicker? Any specific advice at all?