The MaterialThe representation of the surface or volume properties of an object. Layer Group node works with the Layered Material node or it can be connected to an existing material's Material Layer pin (figure 1). It provides additional Layer input pins in the event that all the Layer input pins are in use. Any of the Material Layer nodes can connect to a Layer Group node's Layer input pin, including another Layer Group node. This provides an infinite level of material layering.
Figure 1: A Material Layer Group node is added to an existing Diffuse materialUsed for dull, non-reflecting materials or mesh emitters. node to provide additional material layer inputs