In ProTOp volume regions can only be defined by combining various material regions.
The figures below illustrate a part with three material regions; all three default volume regions and an added combined volume region are shown.
Figure. The list of all volume regions: 3 default regions and 1 added combined region.
Figure. First default volume region - corresponds to first material region.
Figure. Second default volume region - corresponds to second material region.
Figure. Third default volume region - corresponds to third material region.
Figure. Combined volume region: combined second and third material regions.