Aluminum cylinders are usually lined with a steel sleeve to provide a tough wear resistant surface for the piston rings slide against. This type of cylinder however makes for inefficient heat dissipation due to the differing thermal characteristics of the materials. Steel and aluminum have different heat expansion rates thus sometimes hindering the manufacturing process. Additionally, the piston (being aluminum) will also expand faster than the steel sleeve, so that difference must be calculated within the specification for piston-to-cylinder wall clearance. That larger clearance reduces the efficiency of the engine.
A ceramic plated cylinder is an alternative. This eliminates the steel sleeve and, in some designs, inserts an extruded aluminum sleeve that is chemically plated with a very resilient layer of ceramic based material (a carbon/silica mix) to increase wear resistance. An extrusion is used because casting often leaves small air bubbles or other inclusions in the metal surface.
A different design is to use a high-quality die casting for the cylinder which if carefully done, will have minimal air bubbles and a good machined surface. The casting is bored to size, and then plated with the ceramic layer. No sleeve is used at all.
A big advantage of both types of cylinder design is that both the ceramic plated sleeve and actual cylinder are both made of aluminum with very similar (or the same) heat expansion rates. A much reduced and precise gap between piston and cylinder is maintained resulting in much more stable and reliable performance. Weight is also reduced, and excellent oil economy and cooling performance are achieved.