Diffuse Coat Layer

The Diffuse Coat material layer is created with the Add Layer option and cannot be found in the Creation menu of V-Ray Asset Editor.

Diffuse Coat

Color – Specifies the color of the material. For dielectric materials this is the diffuse color. For metals this is the specular reflections color.

Diffuse Roughness – Controls the Diffuse BRDF Falloff. It can be used to simulate rough surfaces or surfaces covered with dust (for example, skin or the surface of the moon). Note that this parameter only affects the diffuse portion of non-metallic materials.

Opacity

Opacity – Specifies how opaque or transparent the material is. A texture map can be assigned to this channel. 

Custom Source – When enabled, V-Ray uses an alpha channel to control the material opacity. 

Diffuse Texture Alpha – The diffuse texture alpha channel controls the opacity. Diffuse Texture Alpha source works the same way as Diffuse Map Alpha as Transparency legacy option from the V-Ray versions before 3.60. 
Opacity Texture Alpha – The opacity texture alpha channel controls the opacity, instead of the default texture intensity. If there is no texture in the source slot, the option is ignored. 

Mode – Controls how opacity is sampled.

Clip – (Very fast) The surface is shaded as either fully opaque or fully transparent depending on the value of the opacity map (i.e. without any randomness). This mode also disables the filtering of the opacity texture. This is the fastest mode but it may increase flickering when rendering animations.
Stochastic – (Optimal) The surface is randomly shaded as either fully opaque or fully transparent so that on average it appears to be with the correct transparency. This mode reduces lightning calculations but might introduce some noise in areas where the opacity map has gray-scale values. The opacity texture is still filtered as normal.

Multipliers

Mode – Specifies how textures and colors will be blended by the multipliers.

Multiply – The texture is blended with a black color.
Blend Amount – The user-specified color is used for blending

Color – Controls the intensity of the Diffuse color.

Opacity – Controls the intensity of the overall material Opacity.