Coat Color – Determines the coat layer's color. The Coat Color tints all layers - reflection, sheen, diffuse and refraction. Note that the coat specular highlights are not affected and are always white. A texture map can be used here.

Amount – Specifies the blending weight of the coat layer. A value of 0 does not add a coat layer, while higher values blend the coat gradually. See the Coat Amount example below for more information.

Coat glossiness – Controls the sharpness of reflection. A value of 1.0 means perfect glass-like reflection; lower values produce blurry or glossy reflections. See the Coat Glossiness example below for more information.

IOR – Specifies the Index of Refraction for the coat layer.

Lock coat bump to base bump – When enabled, it prioritizes the base bump map during rendering over the coat bump map. You can use it to temporarily hide the coat bump.

Bump Map Type –  Allows the user to specify whether a bump map or a normal map effect is added.

Bump Map
Normal map in tangent space
Normal map in object space
Normal map in screen space
Normal map in world space
Local space bump map

Bump Map – Specifies the bump/normal map used as a coat bump.

Coat Bump Mult – A multiplier for the bump effect.

Example: Coat Amount

This example shows how the Amount value affects the look of the material. The base Reflection Glossiness is 0.76 and the Coat glossiness is set to 0.985. IOR is 2.2 and the Coat Color is the default white. 

Example: Coat Glossiness

Coat glossiness controls the sharpness of the coat reflection. In this example, the base Reflection Glossiness is set to 0.76 and the Coat Amount is set to 1. IOR is 2.2 and the Coat Color is the default white. Notice how higher values produce glossier reflection and lower values make it look blurry.