The Null material node is used for mesh objects that have an invisible surface but contain a medium. This is equivalent to setting up a specular material with IOR 1 and a reflection of 0 and a transmission of 1. However, that methodology no longer makes sense with nested dielectric. The Null MaterialThe representation of the surface or volume properties of an object. was created to make a medium with no surface work in all cases.
Figure 1: The Null material with an Octane ScatteringDefines how fast light gets scattered when traveling through the medium. Medium connected to it's Medium input
Medium - Accepts any medium node.
Opacity - Controls the transparency of the material via a greyscale texture.
Affect Alpha - If enabled, refractions will affect the alpha channel.
DisplacementThe process of utilizing a 2D texture map to generate 3D surface relief. As opposed to bump and normal mapping, Displacement mapping does not only provide the illusion of depth but it effectively displaces the actual geometric position of points over the textured surface. - Accepts any displacement node to create highly detailed geometry with a low memory footprint.
Smooth - If disabled, normal interpolation will be disabled and triangle meshes will appear facetted.
Smooth Shadow Terminator - If enabled, self-intersecting shadows are smoothed according to the polygon's curvature.
Round Edges - This creates a shader effect at render time that rounds the sharp edges of objects without modifying and reloading the geometry. Higher values will round the edges more. This is useful to bevel hard edges during render time, like when using low-polygon models. This node is located under the Procedurals section.
Priority - Used to resolve the ambiguity in overlapping surfaces, the surface priority control allows artists to control the order of preference for surfaces. A higher number suggests a higher priority for the surface material, which means it is preferred over a lower priority surface material if a ray enters a higher priority surface and then intersects a lower priority surface while inside the higher priority surface medium.