Pure polyester felt chopped into random sized pieces. This is a premier riding arena fibre additive used for top-level performance sport globally including the Athens 2004 Olympics Games. Unlike many other fibres, because it is pure polyester it has high tensile strength and durability.
Appearance-wise it complements the sand component of your arena. It offers excellent energy return and cushioning and also traps moisture to keep the sand firm, and reducing the need for irrigation.