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The Hair material is primarily designed for rendering hair and fur. The material is based around three components: a primary specular component, a secondary specular component, and a transmission component. A diffuse component is also provided for rendering of materials made up of cloth threads or other non-translucent fibers.

The primary specular component represents light that is reflected off the outer surface of a hair strand. The secondary specular component represents light that goes through the hair strand and is reflected off the back surface. The transmission component represents light that goes through the hair strand.

The image below illustrates the meaning of the three components:

Please note that V-Ray Hair material does not produce hair strands. You can use V-Ray Fur/Grass to procedurally create fur, hair or grass. V-Ray Fur/Grass produces flat strands if Hair material is applied to it.

Some parameters are only available in Advanced mode.

Overall Color – A common color multiplier for all color components in the material (except for opacity). Used to easily change the look of the entire hair material.

Transparency – Controls the transparency of the material. Making the hair more transparent towards the tip may produce more smooth and realistic anti-aliasing at the expense of increased render times. If you map the tip opacity, make sure you do not make the strands thinner at the tip as well - transparency already creates the effect of thinning strands. You can enable the Opaque Shadows and Opaque GI options to reduce render times for transparent hair. Note that with transparent strands, it may be necessary to increase the Max. Transp. Levels option in the Global Switches rollout of the V-Ray settings too.

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Color – Controls the diffuse component of the shader. Use this for materials made out of cloth threads or other non-translucent fibers, as well as for dirty hair. Note that clean hair or fur does not normally have a diffuse component, so in such a case, leave the parameter black.

Amount – The amount of the diffuse component of the material.

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Color – The primary specular color component, which corresponds to light that is reflected off the outer surface of hair strands (see the figure above). Normally this is dark gray.

Amount – A multiplier for the primary specular color.

Glossiness – The glossiness for the primary specular component. Values closer to 1.0 make the hair shinier and sleeker. Lower values give it a matted look.

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Lock to Transmission – When enabled (the default), the color for the secondary specular component is derived from the color of the transmission component. Since a ray of light goes twice through the hair width, the color of the secondary specular component can be computed by multiplying the transmission color with itself. When this option is enabled, the hair color is mostly determined by the Transmission color component.

Color  – The color of the secondary specular component, which corresponds to light that is reflected off the back surface of the hair strands. If Lock to Transmission is enabled, this value is ignored and the secondary specular color is derived from the Transmission color.

Amount  – A multiplier for the secondary specular component. If  Lock to Transmission is enabled, this value is ignored and the secondary specular amount is derived from the transmission amount.

Glossiness – The glossiness for the secondary specular component. Values closer to 1.0 correspond to shiny and sleek hair. Lower values correspond to matted hair.

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Color – The color for the transmission component, which corresponds to light that goes through the hair strands. When Lock to Transmission is enabled, this color determines the overall hair color.

Amount – The amount of the transmission component.

Glossiness L/W – The glossiness of the transmission along and across the hair strand length. For more information, see the Transmission Glossiness Length and Width Parameters example below

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Opaque Shadows – – When enabled, the hair material is always opaque for shadow calculations. This speeds up the rendering of transparent hair.

Opaque for GI – – When enabled, the hair material is always opaque for GI calculations. This speeds up the rendering of transparent hair. For more information, see the Opaque for GI example below.

Simplify for GI – When enabled, a simplified diffuse version of the BRDF is used for GI calculations. This may speed up the rendering of hair but may significantly change the final look.

Use Cached GI – Similar to the Use Irradiance Map option for the VRayMtl Generic material; if it is disabled, the hair material is always calculated with brute force GI. 

Light Multiplier – In the absence of GI, the hair may look very dark. GI is the proper way to correct this, but if GI must be really avoided, this multiplier can be used to brighten the hair.

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Mode – Specifies one of the following methods for adjusting textures.

Multiply –  – Multipliers can be specified to adjust colors and textures.
Blend Amount –  – Blend amounts can be specified to adjust colors and textures.

Overall Color –  – Controls the intensity of the Overall Color, which acts as a color multiplier for all color components in the material.

Transparency – Controls the intensity of the Transparency.

Diffuse Color – Controls the intensity of the diffuse component color of the shader.

Primary Spec. Color – Controls the intensity of the Primary Specular color component, which corresponds to the light reflected off the outer surface of the hair strands.

Secondary Spec. Color  – Controls the intensity of the Secondary Specular color component, which corresponds to the light reflected off the back surface of the hair strands.

Transmission Color – Controls the intensity of the Transmission color component, which corresponds to the light that passes through the hair strands.