Selection of materials for an indoor horse riding arena can be a daunting task. There may be advantages and disadvantages to each respective material. This makes it more difficult when considering a universal recommendation that is most appropriate for choosing the best riding arena surface or footing material. In addition, materials available may be dependent on what is locally available as well as transportation expense when considering cost.  

Points of consideration: 
The base material needs to be compacted as densely as possible to provide a stable material for hoof and tractor pressure. The base is typically a 4 to 6 inch layer of material. A limestone mix no larger than 3/8 inch will make a good base. Another option for a suitable base from a natural soil perspective would be something that has mostly clay content that is easily compacted.
The top footing surface is typically 2 to 6 inches thick. However, if choosing to use sand as the top footing surface, start with a 2 inch layer then add or replace a 1/2 inch at a time as needed (no deeper than 4 inches). A sand, footing surface that is too deep is stressful on horse tendons. A few specifications when choosing sand as a riding arena surface material include: clean, screened and angular. "Clean or washed" meaning that the material has been washed of silt and clay, making it less dusty and less compactable. "Screened" is essentially removing the larger, undesirable particles from the material making it more difficult to compact. "Angular" sand particles will provide better traction and may last longer than a sand with round particles.