I will not be able to talk about Metal, do not listen to it at all. The material of the cans is unpainted black matte plastic. My HD650 is fully broken in with hundreds of hours playing time, the HD660S is brand new. Let's wait with too much talk about sound details. They are for sure much more efficient and herewith easier to drive than HD650. The foam feels harder, but still comfy. The material covering the foam is identical to the HD650.