The VRay Fresnel node is used to output Fresnel values. The most common use is to be rendered as a separate Render Element to then be used in compositing. To do so, go into the Render Settings window and in the Render Elements tab create an Extra Tex node. Once created, select it and in the Attributes Editor, under “Extra Attributes” create a node for the Vray Texture Extratex attribute and choose VRay Fresnel.

What is Fresnel?

Look through a window while standing right in front of it and notice how little or no reflections are visible. Then move aside and try looking through it from a very low angle, you’ll realize that the window has become almost purely reflective and you can’t see through it anymore. This is the principle of Fresnel.

In a few words, every material’s reflections and refractions intensity change according to the angle at which they’re being seen at. VRay shaders already have this phenomenon integrated, for example the VRay Mtl shader already has the option “Use Fresnel” activated to respect the realism of materials.

Parameters

1
0
360
0

Front Color

“Front Color” is the color of the surface facing the camera at perpendicular angles.

1
0
360
360

Side color

“Side Color” is the color of the surface facing the camera at low angles.

1
1
10
1

IOR

“IOR” stands for Index Of Refraction and controls how much light is deviated when bouncing off a reflective material. A value of 1 causes no change in direction, meaning that it has the same density as air. Values slightly above 1 are soft materials that are almost non reflective from the front but from the side. An example of this can be skin, cloth etc. The harder and the more reflective the material becomes, such as metals, the higher the IOR, meaning that it reflects more uniformly from each angle, independently from which angle it’s viewed. An example of a very high IOR is mirror, in fact it is always purely reflective.