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The V-Ray BRDFVRayMtl provides inputs for controlling various material properties. They correspond to parameters in the section below.

Diffuse

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Color – The Specifies the diffuse color of the material. Note: the actual diffuse color of the surface also depends on the reflection and refraction colors.

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Opacity – Assigns opacity to the material where 1.0 is completely opaque and 0.0 is completely transparent.

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Normal –  The opacity map is evaluated as normal: the surface lighting is computed and the ray is continued for the transparent effect. The opacity texture is filtered as normal.
Clip – 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 might increase flickering when rendering animations.
Stochastic – 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 lighting calculations but might introduce some noise in areas where the opacity map has gray-scale values. The opacity texture is still filtered as normal.

Self-illumination – The Specifies the self-illumination color of the material.

Self-illumination Mult. – A Specifies a multiplier for the self-illumination of the material.

Self-illumination Affects Gi – When enabled, the self-illumination color affects GI computations.

Reflection

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Brdf Type – Determines the type of BRDF (the shape of the highlight and glossy reflections). This parameter has an effect only if the Reflection Color is different from black and Reflection Glossiness is different from 1.0. For more information, see The BRDF Type example below.

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Glossiness – Controls the sharpness of reflections. A value of 1.0 means 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. For more information, see The Reflection Glossiness Parameter example below.

Lock Highlight Glossiness – When disabled, the user can enter different values for the Hilight Glossiness and Reflection Glossiness. However this does not produce physically correct results.

Highlight Glossiness – Determines the shape of the highlight on the material. Normally this parameter is locked to the Reflection Glossiness value in order to produce physically accurate results.

Use Fresnel – 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 (IOR) as well.

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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.

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Anisotropy – Determines the shape of the highlight. A value of 0.0 means isotropic highlights. Negative and positive values simulate "brushed" surfaces. For more information, see the Anisotropy example below.

Rotation – Determines the orientation of the anisotropic effect in a float value between 0 and 1 (where 0 is 0 degrees and 1 is 360 degrees). For more information, see Anisotropy Rotation example below.

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This example demonstrates the differences between the BRDFs available in V-Ray. Note the different highlights produced by the different BRDFs. The Reflection Glossiness is set to 0.8.

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Glossiness – Controls the sharpness of refractions. A value of 1of 1.0 means 0 means perfect glass-like refraction; lower values produce blurry or glossy refractions. Use the Refraction Subdivs parameter below to control the quality of glossy refractions. For more information, see The Refraction Glossiness Parameter example below.

Index of Refraction – Index of refraction for the material, which describes the way light bends when crossing the material surface. A value of 1.0 means the light does not change direction.  For more information, see The Refraction IOR Parameter example below.

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This example demonstrates the effect of the Refraction IOR parameter. Note how light bends more as the IOR deviates from 1from 1.0. The case when the index of refraction (IOR) is 1is 1.0 produces 0 produces a transparent object. Note however, that in the case of transparent objects, it might be better to assign an opacity map to the material, rather than use refraction.

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Fwd / Back coeff – Controls the direction of scattering for a ray. A value of 1.0 means a ray can only go forward (away from the surface, inside the object); 0 0.5 means 5 means that a ray has an equal chance of going forward or backward; 0.0 means a ray is scattered backward (towards the surface, to the outside of the object).

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Scatter Coeff – The amount of scattering inside the object. A value of 1.0 means 0 means rays are scattered in all directions; 0.0 means 0 means a ray cannot change its direction inside the sub-surface volume.

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Options

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Cutoff – A threshold below which reflections/refractions is not traced. V-Ray tries to estimate the contribution of reflections/refractions to the image, and if it is below this threshold, these effects are not computed. Do not set this to 0.0 as it may cause excessively long render times in some cases.

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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.

Use Irradiance mapMap – When enabled, the irradiance map is used to approximate diffuse indirect illumination for the material. If disabled, Brute Force GI is used in which case the quality of the Brute force GI is determined by the Subdivs parameter of the Irradiance Map. This can be used for objects in the scene which have small details that are not approximated very well by the irradiance map.Fix Dark Edges – When enabled, fixes the dark edges that sometimes appear on objects with glossy materials.

Energy Preservation – Determines how the diffuse, reflection, and refraction color affect each other. V-Ray tries to keep the total amount of light reflected off a surface to less than or equal to the light falling on the surface (as in the real life). For this purpose, the following rule is applied: the reflection level dims the diffuse and refraction levels (a pure white reflection will remove any diffuse and refraction effects), and the refraction level dims the diffuse level (a pure white refraction color will remove any diffuse effects). This parameter determines whether the dimming happens separately for the RGB components or is based on the intensity:

Monochrome – Causes dimming to be performed based on the intensity of the diffuse/reflection/refraction levels.
Color – Causes dimming to be performed separately on the RGB components. For example, a pure white diffuse color and pure red reflection color will yield a surface with a cyan diffuse color (because the red component is already taken by the reflection).

Glossy Rays as As GI – Specifies on what occasions glossy rays are treated as GI rays:

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Refl. Gloss. Interpretation –These options control how Reflection Glossiness is interpreted. When Use Glossiness is selected, the Glossiness value is used as is, and a high Glossiness value (such as 1.0) results in sharp reflection highlights. When Use Roughness  is selected, the Reflection Glossiness  inverse value is used. For example, if Reflection Glossiness  is set to 1.0 and Use Roughness  is selected, this results in diffuse shading. Conversely, if Glossiness is set to 0.0 and Use Roughness is selected, this results in sharp reflection highlights. Note that the Roughness parameter itself has no bearing on the results of this option. 

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