This is one of Thor’s crossover products from their moto ranges. It’s made up of thick Airprene (a less dense form of neoprene), with an external hard plastic knee cup and internal shin guard.
They're designed to go under riding kit, but in reality they are too bulky for pedalling under all but the baggiest strides. The upper Velcro closure also chafes round the back of the knee.
The hefty, full wrap-around coverage and serious knee and shin impact protection are well suited to freeride use, because things get pretty warm in there for any pedalling action.