The Wrapper Material can be used to specify additional surface properties per material.
Wrapper Material Parameters
Base material – Specifies the surface material.
Alpha contribution – Determines the appearance of the object in the alpha channel of the rendered image.
Normal (1) – A value of 1.0 means the alpha channel will be derived from the transparency of the base material.
Ignore in Alpha (0) – A value of 0.0 means the object will not appear in the alpha channel at all and will show the alpha of the objects behind it.
Black Alpha (-1) – A value of -1.0 means that the transparency of the base material will cut out from the alpha of the objects behind. Matte objects are typically given an alpha contribution of -1.0. Note that this option is independent of the Matte surface option (i.e. a surface can have an alpha contribution of -1.0 without being a matte surface).
Matte – When enabled, the material appears as a matte material, which shows the background, instead of the base material, when viewed directly. Note that the base material is still used for things like GI, caustics, reflections etc.
Matte for Secondaries – Normally the base material will be used when an object with a Wrapper Material is seen through reflections/refractions. When enabled, the Wrapper Material will show the environment when seen through reflections/refractions, and the environment map will be projected on the matte geometry.
All secondary rays (reflections and refractions)
Project environment map on the matte geometry
No GI on Other Mattes – When enabled, the object appears as a matte object in reflections, refractions, GI, etc. for other matte objects. Note that if this is on, refractions for the matte object might not be calculated (the object will appear a matte object to itself and will not be able to "see" the refractions on the other side).
Shadows – When enabled, shadows are visible on the matte surface.
Shadow Tint – Specifies a tint for the shadows on the matte surface.
Shadow Opacity – Specifies an optional brightness value for shadows on the matte surface. A value of 0.0 makes the shadows completely invisible, while a value of 1.0 produces the full shadows.
Affect alpha – When enabled, shadows affect the alpha contribution of the matte surface. Areas in perfect shadow will produce white alpha, while completely unoccluded areas will produce black alpha. Note that GI shadows (from skylight) are also computed. However, GI shadows on matte objects are not supported by the photon map and the light map GI engines when used as primary engines. Those with matte surfaces can be safely used as secondary engines.
Generate GI – Controls the Global Illumination created by the material.
Receive GI – Controls the Global Illumination received by the material.
GI Quality Multiplier – Specifies the quality of GI for specific objects and allows adjustments to the render quality.
Generate caustics – When enabled, the material will generate caustics.
Receive caustics – When enabled, the material will receive caustics.
Can be Overridden – When disabled, the material is not overridden by the Material Override option in the Render Settings.