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.
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]
A gray scale map should be connected (through a Range shader) to Thin Film Thickness if variation in the Thin Film is required.
More Information about soap bubble color and film thickness can be found here.
Thin Film can also be used for other materials, such as multi-tone car paint or the reflective, colored coating on a beetle (Thickness: 400, IOR: 1.43).