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Every realistic material has its own index of refraction (IOR) When transparent, the material IOR is used to deviate light rays when they travel through the volume (see figure below).
The same realistic material with two different IOR values (1.02 on the left and 1.1 on the right) As for reflections, refractions can be glossy to simulate a wide range of materials:
The same realistic material with (on the right) or without (on the left) refraction glossiness
The Bidirectional Reflectance Distribution Function is a function that defines how light is reflected at an opaque surface.
BRDF - Reflection
This group lets you set the glossiness parameter of reflection. The glossiness parameters control how much the reflections/transmissions are blurry. Depending on the chosen glossiness values, the results may vary a lot:
Different reflection glossiness settings Glossiness is achieved by increasing the "Anisotropy in U" and "Anisotropy in V" parameters. If both parameters are identical, then, the reflection is isotropic. If both parameters have different values, the reflection is anisotropic, like on a CD-ROM surface or on hairs and furs.
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Like for the BRDF - Reflection group, this one lets you set the glossiness parameter for the transmission. The IOR (Index Of Refraction) is exposed to control the amount of refraction.
A transparent material with different IOR
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