Most high-end deck projects use closed risers to finish the stairs. Open risers sometimes appear cheap and unfinished. They are also often in violation of IRC code for decks over 30", which maintains that they meet the same requirements as guardrail infill. Stair risers may not have openings present that would allow a 4” diameter sphere to pass through. Most risers are made from deck boards or fascia material. Make sure the material is heavy duty enough to resist feet kicking the risers. If you are using 1x material you may want to install blocking behind the riser board for added strength. Low voltage lights can be installed into the riser boards in order to meet the IRC code for stair illumination. Most deck stairs use a nosed tread that extends beyond the riser board which looks attractive and protects it from being kicked loose from above.