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 (0 to 2000 (soft min/max)). This affects the specular, transmission and coat components. Normally this would be something like a noise map to give some variation to the interference effect. If the thickness becomes large like 3000 [nm], the iridescence effect will disappear, which is a physically correct behavior.
A gray scale map should be connected (through a Range shader) to Thickness if variation in the Thin Film is required.
The refractive index of the medium surrounding the material. Normally this is set to 1.0 for air.
The IOR for water is 1.33 and soap is about 1.5. Therefore the IOR for a soap bubble should be in the 1.33-1.4 range.
Specular Color: 1 1 1
Specular Roughness: 0
Specular IOR: 1.0
Transmission Color: 1 1 1
Coat IOR: 1.5
Thin Film: IOR 1.4
Thin Film Thickness: 500 [nm]
More Information about soap bubble color and film thickness can be found here.
Thin Film can be used for materials other than bubbles. For example, in the image below it has been used to represent the colored reflective coating on a beetle.