Mine is an aluminum diamond plate panel. It matches my aluminum corner guards.
Trick is, after you install the sliders, run a thin bead of silicone or black permatex along the top edge to keep water from getting behind the slider and getting trapped in there and rusting or rotting your rocker panel out. I actually have a bead run around the entire perimeter of the slider to keep moisture out.
'87 YJ, 4.2L built and bored, 8.5" of lift, 8.8 rear, AX15/NP 231, Tom Woods drive shafts, Flat fenders, 12,000LB winch, Custom bumpers, Rattle can paint job. Never completed...