This member cannot be used in scripts, but is usable in the command bar.
This property determines the apparent roughness across the surface. A roughness map is a grayscale image where black pixels correspond to a maximally smooth surface, and white pixels correspond to a maximally rough surface.
Roughness refers to how much variation the surface has on a very small scale. Reflections on smooth surfaces are sharp and concentrated. Reflections on rough surfaces are more blurry and dispersed.