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BRDF Type – Determines the type of BRDF (the shape of the highlight). 

GGX – GGX Microfacet highlight/reflections. Specular highlights have a bright center with a longer falloff.
Phong – Phong highlight/reflections. Specular highlights have a bright center with no falloff.
Blinn – Blinn highlight/reflections. Specular highlights have a bright center with a tight falloff.
Ward – Ward highlight/reflections. Specular highlights have a bright center with a falloff broader than Blinn, but tighter than Microfacet GTR (GGX).

Color – Specifies the reflection color of the material. Note that the reflection color dims the diffuse surface color. 

 Glossiness –  Controls the sharpness of reflections. A value of 1.0 means perfect mirror-like reflection; lower values produce blurry or glossy reflections. Use the Reflection Subdivs parameter below to control the quality of glossy reflections.

 GGX Tail Falloff – Controls the transition from highlighted areas to non-highlighted areas when the BRDF Type is set to GGX.

Metalness – Controls the reflection model of the material from dielectric (metalness 0.0) to metallic (metalness 1.0). Note that intermediate values between 0.0 and 1.0 do not correspond to any physical material. This parameter can be used with PBR setups coming from other applications. The reflection color should typically be set to white for real world materials.

GTR Energy Compensation – Compensates GTR lost energy and an accurate Fresnel formula for conductors is used for metals. This option is enabled by default for all newly created materials and is hidden from the UI. It is also hidden for Cinema 4D S24 and older versions, where it is forcefully enabled. It is visible in all other older scenes.

Use Roughness –  This option controls how Glossiness is interpreted. When Use Roughness is selected, the Glossiness inverse value is used. For example, if Glossiness  is set to 1.0 and Use Roughness is selected, this will result in diffuse shading. Conversely, if Glossiness is set to 0.0 and Use Roughness is selected, this will result in sharp reflection highlights. 

Fresnel

Fresnel Reflections — When enabled, makes the reflection strength dependent on the viewing angle of the surface. Some materials in nature (glass etc) reflect light in this manner. Note that the Fresnel effect depends on the index of refraction as well. S

Lock Fresnel IOR – Allows the user to unlock the Fresnel IOR parameter for finer control over the reflections.

Fresnel IOR –  The Index of reflection to use when calculating Fresnel reflections. Normally, this is locked to the Refraction IOR parameter, but you can unlock it for finer control.

Anisotropy

Anisotropy (-1..1) –  Determines the shape of the highlight. A value of 0.0 means isotropic highlights. Negative and positive values simulate "brushed" surfaces. 

Anisotropy Rotation – Determines the orientation of the anisotropic effect in a float value between 0.0 and 1.0 (where 0.0 is 0 degrees and 1.0 is 360 degrees). 

UV Vectors Derivation – Specifies the method for deriving anisotropy axes:

Local object axis – Uses a local axis for the anisotropy effect. 
Specified UVW generator – Allows the user to assign a UVW Generator for the anisotropy effect.

Anisotropy Axis – Specifies a local object axis for the anisotropy effect when UV Vectors Derivation is set to Local object axis.

Thin Film

Enable Thin Film – Enables the Thin Film parameter.

Thickness Min (nm) – Determines the minimum thickness of the thin film in nanometers. If no Thickness Blend is applied, only this value is used for the thickness of the thin film.

Thickness Max (nm) – Determines the maximum thickness of the thin film in nanometers. This option is only available when Thickness Blend is applied.

Thickness Blend – Allows a map to be attached that blends the thickness values. If no map is applied, only the Min Thickness value is used to determine thickness.

Thin Film IOR – Specifies the reflective index of the thin film. A texture can be attached to this slot.

Texture – Specifies a texture file to be used for the Thin Film IOR.

Mix Strength – Specifies the blend amount for the texture file.

Reflection Advanced

Trace Reflections – Check this option to enable reflections for the material.

Max Depth – The number of times a ray can be reflected. Scenes with lots of reflective and refractive surfaces may require higher values to look correct.

Enable Dim Distance – Allows you to stop tracing reflection rays after a certain distance.

Dim Distance – Specifies a distance after which the reflection rays will not be traced.

Dim Fall-off – A fall off radius for the dim distance.

Reflect on Back Side – When disabled, V-Ray calculates reflections for the front side of objects only. Checking it makes V-Ray calculate the reflections for the back sides of objects too.

Soften – Softens the edge of the BRDF at light/shadow transitions.

Affect Channels – Specifies which channels are affected by the reflectivity of the material.

Color Only – The reflectivity will affect only the RGB channel of the final render.
Color+alpha – Causes the material to transmit the alpha of the reflected objects, instead of displaying an opaque alpha.
All channels – All channels and render elements will be affected by the reflectivity of the material.