Define one of the two types of surface masks: outside or inside.
When you define a mask as an outside type, the portion of the surface outside the defined polygon is hidden (the outside display is clipped to the mask segments):
When you define a mask as an inside type, the portion of the surface residing inside the defined polygon is hidden:
When you define an inside or outside mask as render only, the specified render material is applied to the inside or the outside of the mask polygon. The display of the surface is not masked, but when the surface is rendered, the render material pattern is displayed. The following illustration shows the render material applied to an inside mask:
