Compound materials combine two or more sub-materials for a variegated look, especially when used with maps.
Compound materials are similar to compositor maps, but they exist at the material level. You load or create compound materials using the Material/Map Browser.
Different types of materials create different effects, behave in particular ways, or are provided as ways to combine multiple materials.
The sub-materials of a compound material can be either photometric or non-photometric. All sub-materials in the compound should be of one type or the other.