The Metallic input controls how 'metal-like' your surface will be. Nonmetals have Metallic values of 0 and metals have Metallic values of 1. For pure surfaces, such as pure metal, pure stone, pure plastic, etc. this value will be 0 or 1, not anything in between. When creating hybrid surfaces like corroded, dusty, or rusty metals, you may find that you need some value between 0 and 1.
