Aluminum Composite Panels, AKA "ACM" If Oil Canning or waviness in sheet metal bothers you, ACM is a good option @ 4mm thick there is virtually no oil canning. over 200 colors and finishes available. This product needs to be CNC Routed and programmed on CAD "Route and Return Method" Not for the faint of heart or tight budgets, Currently at approximately $75.00 to $80.00 Per square foot.