Just to add a wee bit more to my earlier post… I think this stuff can be a bit counterintuitive. If you want to get good protection from a thin pad, that tends to mean making it denser and stiffer, which means it’s less comfortable and harder to keep on. So you end up with more straps and a bigger “sock” which ironically makes them sweatier. Whereas a big flexible pad can move better with the arm or leg and ends up bulky but comfier.
The best example I have of that is my elbow pads, POC Bones. They’re massive, proper DH protection but because they’re big and articulated and move well with the arm, they barely need held on at all- there’s a very light, loose “sock” and 2 loose straps and that’s it. So they’re cooler and comfier than any other pad I’ve ever tried. But look like cricket pads.
Coverage is important too… Kneecap cover is obvious and I think all pads do that as a priority but some of the worst knee knocks I’ve had have been to the side of the knee, from the top tube sometimes or from the ground. And it’s pretty amazing how many pads have no side protection at all, or little bits away from the joint but none on the joint itself. That’s something well worth having imo, a pad without it is just much less likely to be useful. And again there’s not much downside to it.