Understanding the metallic setup

Unity provides three different types of PBR shaders; they are referred to in the drop-down menu of the material's Inspector tab as Standard, Standard (Roughness Setup), and Standard (Specular setup). The main difference is that Standard and Standard (Roughness Setup) expose the Metallic property, but Standard contains a Smoothness property while the second replaces Smoothness with Roughness. Standard (Specular setup) contains Smoothness, but replaces the Metallic property with Specular. Smoothness and Roughness are opposites of each other, so a 1Smoothness means 0Roughness and vice versa. You can generally get the same result no matter which shader you use, so it mostly comes down to personal preference.

These setups represent different ways in which you can initialize PBR materials. One of the concepts that has driven PBR is the ability to provide meaningful, physically-related properties that artists and developers can tweak and play with. The properties...