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The Transmission material is special material simulating transmissive surfaces. The material can emit refractive caustics and allows you to choose between different BRDFs using the Brdf attribute. It should be blended with a diffuse and reflective materials since it lacks a diffuse/reflection component.

Transmission Material


The color of the material is the color of the light path when it exits the surface after it has been transmitted from the material. The direction of the transmitted light path is directly dependent of the Index of Refraction (IOR) attribute.

Attribute Description
Color Define the color of the transmission.
Gain Set the gain of the transmission color.
Exit Color Define the color returned by the path tracer when the path has reached the maximum refraction depth set in the path tracer. This is useful is some complex rendering scenarios such as when rendering a crystal like materials.
Index of Refraction Define the index of refraction of the surface.

Color 10 00 00

Color 00 10 00

Color 00 00 10

Color 10 10 00

Color 00 10 10


Gain 0%Gain 0%

Gain 25%

Gain 50%

Gain 75%Gain 75%

Gain 100%

Index of Refraction#

IOR 10

IOR 125

IOR 15

IOR 175

IOR 20


The material supports Roughness, Anisotropy and multiple microfacet models that can be selected using the Btdf attribute.

BTDF Description
GGX GGX distribution results are very close to empirical data.
Beckmann Beckmann distribution tends to provide sharper reflections when compared to GGX

Roughness 0%

Roughness 25%

Roughness 50%

Roughness 75%

Roughness 100%


Anisotropy control how much the specular highlight is stretched along a direction defined by Anisotropy Space.

  • When set to Tangent UV the material uses a frame defined by the UV mapping of the texture connected to the Anisotropy Direction, Anisotropy Rotation, Anisotropy, Roughness or Color attributes.
  • When set to Tangent Parametric the material uses the surface parametric frame whereas in Object it uses the frame defined by the object. Anisotropy Direction defines the direction of the anisotropy on the local surface frame and Anisotropy Rotation defines the rotation of the anisotropy along the direction.

The material below has its Roughness set to 100%

Roughness 100% Anisotropy 0%

Roughness 100% Anisotropy 25%

Roughness 100% Anisotropy 50%

Roughness 100% Anisotropy 75%

Roughness 100% Anisotropy 100%


The Transmittance simulates the density of the dielectric medium filtering the color of ray the further it travels through the material. Transmittance Color defines the reflected color of the medium while Transmittance Density controls the density of the medium which directly translates into the scale factor of the ray attenuation. The higher the value, the more the color of the ray shifts towards the color defined by Transmittance Color.

The material below has a Transmittance Color set to (0.2, 0.6, 0.2)

Transmittance Color 02 06 02 Transmittance Density 0%

Transmittance Color 02 06 02 Transmittance Density 25

Transmittance Color 02 06 02 Transmittance Density 50

Transmittance Color 02 06 02 Transmittance Density 75

Transmittance Color 02 06 02 Transmittance Density 100

Transmission Scattering#

The Transmission Scattering simulates the scattering of light inside the medium turning it as a homogenous volume. The maximum number of bounces of the scattering within the volume is controlled by Volume Depth attribute.

Note that transmission scattering doesn't render properly when the camera is placed inside the medium.