Matrix Pro-Impact Inserts are most suitable for athletic performance and intense schooling. Designed to go inside the Matrix Half Pad. Poron XRD is an ultra-light and ultra-thin layer (5mm) of high density open cell foam that absorbs 90% of the energy from impact.... (read more) It protects the horse's back muscles from the impact of the saddle and minimizes the energy bounce back that the rider experiences when landing in the saddl, allowing for a more secure seat. Superior to heavier and thicker foams and gel, the XRD is perforated for additional breathability. Treated with Microban(R). Sold as a pair. Fits both Traditional and Ergonomic Matrix Half Pads. Dressage.