Nobody likes wearing bulky knee pads, but sometimes you just have to. Until now, that is. POC Joint VPD Knee Protectors provide the protection of a bulky hardshell knee pad with the slim design and breathability of a soft pad. The secret is Visco Elastic Polymer Dough, or VPD. This modified polyurethane foam is soft and pliable. In a hard impact, however, it instantly hardens into a protective shell. These VPD pads are placed in the front and sides of the knee protector and held in place with stretchy, breathable neoprene. High abrasion areas are then covered with an abrasion resistant aramid fabric.