Starting Foil and Finished Surface Copper Thickness
Internal Layers [Non-plated]: Specify starting foil weight. Finished thickness shall be per IPC-6012C table 3-11.
External layers [Also applies to plated internal layers]: Specify EITHER the starting foil weight or finished copper weight (or thickness).
Most PCB fab houses prefer the finished Cu thickness (or weight) to be specified. Finished thickness shall be per IPC-6012C table 3-12.