Thin Film reproduces the effect of thin film interference on a surface.
Defines the actual thickness of the film between the specified min and max thickness values. Normally this would be something like a noise map to give some variation to the interference effect.
The refractive index of the medium surrounding the material. Normally this is set to 1.0 for air.
How Thin Film is Modeled
How to Map IOR values from Thin Film to Standard Surface