Vray Hair Materialis a material that is primarily designed for rendering of hair and fur. The material is based around three components – primary specular component, 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 following image illustrates the meaning of the three components:

HairMtl_1

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.

Basic Properties

Name – here you can enter a name for the object.

Layer – If an element was assigned to a layer its layer color will be displayed here. This field reflects the layer color in the Layer Palette. You can drag & drop layers from the Layer Browser or similar layer fields onto this field. You can also assign layers or remove elements from current layers using the menus located behind the small triangle.

Preview Quality – quality of material preview in preview window.

Overridable – when you use Override material options in Global options, you can specify some materials that will no be override, like glasses, curtains etc..it useful for preview vizualization of interiors.

MatID Color – ID of the material for multipass rendering.

Round Edges – edges of object with this material will be rounded.

Color

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.

Texture Map – here an image texture or shader can be defined.

Transparency – controls the transparency of the material where white is opaque, and black is fully transparent. Making the hair more transparent towards the tip may produce more smooth and realistic anitaliasing at the expense of increased render times. If you map the tip opacity, make sure you don’t make the strands thinner at the tip as well – transparency already creates the effect of thinning strands. You can enable the Opaque for shadows and Opaque for GI options to reduce render times for transparent hair. Note that with transparent strands, it may be necessary to increase the Max transperency levels option in the Global Options too.

Texture Map – here an image texture or shader can be defined.

Use directly Hair color (from root to tip) –  when this option uncheck you can use Diffuse Color to control hair color.

Diffuse 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 that case leave the parameter black.

Texture Map – here an image texture or shader can be defined.

Diffuse Amount – the amount for the diffuse component of the material.

Texture Map – here an image texture or shader can be defined.

Specular

The primary specular component corresponds to light that is reflected off the outer surface of hair strands.

Primary Specular Color – the primary specular color component. Normally this is dark gray.

Texture Map – here an image texture or shader can be defined.

Primary Specular Amount – a multiplier for the primary specular color.

Texture Map – here an image texture or shader can be defined.

Primary Specular Gossiness – the glossiness for the primary specular component. Values closer to 1.0 make the hair more shiny and sleek. Lower values give it a matted look.

Texture Map – here an image texture or shader can be defined.

The secondary specular component corresponds to light that is reflected off the back surface of the hair strands.

Secondary Specular Color – the color of the secondary specular component. If Secondary Specular Lock is enabled, this value is ignored and the secondary specular color is derived from the transmission color.

Texture Map – here an image texture or shader can be defined.

Secondary Specular Amount – a multiplier for the secondary specular component. If Secondary Specular Lock is enabled, this value is ignored and the secondary specular amount is derived from the transmission amount.

Texture Map – here an image texture or shader can be defined.

Secondary Specular 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.

Texture Map – here an image texture or shader can be defined.

Secondary Specular Lock – if this is 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.

Transmisson

The transmission component corresponds to light that goes through the hair strands.

Transmission Color – the color for the transmission component. When Lock to transmission is enabled, this color determines the overall hair color.

Texture Map – here an image texture or shader can be defined.

Transmission Amount – the amount of the transmission component.

Texture Map – here an image texture or shader can be defined.

Transmission Glossiness Length – the glossiness of the transmission along the hair strand length. See the Examples for a demonstration of the effect of this parameter.

Texture Map – here an image texture or shader can be defined.

Transmission Glossiness Width – the glossiness for the transmission component across the hair strand width. See the Examples for a demonstration of the effect of this parameter.

Texture Map – here an image texture or shader can be defined.

Options

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

Opaque for GI – when this is enabled, the hair material is always opaque for GI calculations. This speeds up the rendering of transparent hair.

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 – if it is enabled, the hair material will always be calculated with irradiance map/light cache.

The preferred method for rendering objects with the Vray Hair Material is with GI enabled, Primary engine set to Brute force, and the Secondary engine set to Light cache with the Retrace threshold enabled. Because of the fine details in hair objects, the irradiance map may produce too much flickering in animations.

Global illumination is vital for realistic rendering of hair, especially with bright hair color. Proper gamma workflow is essential for realistic rendering of hair.

Video provided by Josef Bsharah

Example: Transmission Glossiness Length and Width Parameters

This example shows the effect of the Transmission Glossiness Length and the Transmission Glossiness Width parameters. It shows a number of vertical strands (in this case, produced by V-Ray Fur) lit from behind by a sphericallight.

Note how each parameter changes the way light scatters along the length and the width of the strands. Higher values for the length glossiness compress the transmission highlight along the strand length, while lower values expand it.

Length 0.87 Width 0.98

Length 0.87
Width 0.98

Length 0.85 Width 0.95

Length 0.85
Width 0.95

Length 0.95 Width 0.85

Length 0.95
Width 0.85

Length 0.98 Width 0.8

Length 0.98
Width 0.8

Example: Effect of GI on Hair

This example shows how important GI (multiple scattering) is for the appearance of hair, especially bright hair. The top row shows several of the presets rendered without GI, and the bottom shows the same scene when GI is enabled. Again, GI is brute force and light cache has retrace. The scene GIenvironment is black so that a sphericalarea light is the only light source.

GI is Disabled

GI is Enabled

Example: Strand Taper vs Transparency Mapping

This example shows how transparency mapping can be used to simulate hair thinning towards the tips with improved quality. Since transparency also increases render times, the VRayHairMtl material provides two options to optimize this – the Opaque for Shadows and Opaque for GI options allow to skip the transparency calculations for shadow and GI rays, thus speeding up the rendering.

For the first image, the thinning of the strands towards the tips was done by setting the Taper parameter of VRayFur to 1.0. The opacity of the hairs for the 2nd, 3rd and 4th image is done with the VRayHairInfoTex texture in the Opacity slot of the VRayHairMtl material, while keeping the Taper parameter in VRayFur to 0.0. The scene is illuminated with one point light with sharp raytraced shadows to better show the difference between the options. Note how opacity mapping improves the antialiasing of the hair, while still preserving the same overall look, at the expense of somewhat increased render times. However, the first image also required increased AA samples compared to the rest.
Note that using transparency for the strands may require increasing of the Max. Transp. Levels option in the global V-Ray settings, although it was not necessary for this particular case.

Hair geometry with taper. Render time: 1m 6s

Hair geometry with taper.

Render time: 1m 6s

Hair geometry without taper, with opacity mapping. Render time: 2m 14s

Hair geometry without taper, with opacity mapping.
Render time: 2m 14s

Hair geometry without taper, with opacity mapping, both Opaque for Shadows and Opaque for GI enabled. Render time: 1m 46s

Hair geometry without taper, with opacity mapping, both Opaque for Shadows and Opaque for GI enabled.
Render time: 1m 46s

Hair geometry without taper, with opacity mapping, Opaque for GIenabled, Render time: 1m 57s

Hair geometry without taper, with opacity mapping, Opaque for GIenabled,
Render time: 1m 57s