Erik Selin writes:
In this post, physically based rendering and Blender materials, we looked at how the principled shader really works. We lay the foundation for our future material creation in Cycles and for Eevee when Blender 2.8 finally arrives. Here, we will take a close look at how this is all implemented in the node editor using image textures to power the principled shader. This setup will then be supported by various other nodes to give us a system to work with when layering different materials on top of each other.