1. I am using subsurface scattering node in cycles and want to change IOR of mesh (human muscle). But there is no option to do so. IOR option comes with Glass BSDF node but it changes my mesh appearance. Is there anyone how to to that?
  2. Does anyone know physical background (formulas, or law) behind subsurface scattering node in cycles. How much light will penetrate, etc? I checked in blender wiki but it is not stated there. Thanks
  • $\begingroup$ Refraction is when light get bent while traveling through an object. Subsurface scatering is when light enters the mesh and gets scattered inside. It does not "pass through" so to speak. there for their is no IOR(index of refreaction). Besides, refraction on a human muscle would just look plain weird... $\endgroup$ – GiantCowFilms Jul 16 '14 at 15:00
  • $\begingroup$ Try using a Fresnel node. $\endgroup$ – user1853 Jul 16 '14 at 15:21

Well, I'm really happy that you asked this question. I decide to try using the Fresnel Input Node to modulate the various Input sockets of the SSS shader and the results are interesting. Using Fresnel for the radius adds depth, but it does dampen the SSS effect for the front facing poly's, so maybe it would be better to mix this setup with a stock SSS node. Using 3 Fresnel Nodes with different IOR values and a Combine node for the Radius not only adds depth but adds a tone gradient which makes the SSS results interesting I think.

Here is a basic setup which uses a model that I recently rebuilt for someone so it can be used with Cycles bake.

There is an Environment Texture set to a value of 3 and a front facing overhead sun light at about 11:00.

The model on the Left uses a stock SSS shader with radius values of 0.9, 1.5, 0.7. for the hair. The values are 2.0, 1.45, 0.35 for the face.

The model in the center uses a Fresnel node plugged directly into the Radius of an SSS node so all 3 values have the same input.

The model on the right uses 3 separate Fresnel nodes to control the 3 values of Radius for the SSS node. The Fresnel values are the same as the radius values for the model on the left.

It's subtle and mostly just visible at the edges the way I did it here, but if you put some effort into it you may get somewhere with this.

enter image description here


For materials like skin you don't use index of refraction but you use index of reflection. You can achieve this by mixing your sss node with a glossy shader and change the amount of 'glossyness' as you like. Then you plug a color mix into the roughness value of the glossy node. Then you plug in a fresnel node with the IOR value you want into the factor. Then if you change the value of your two colors you are able to control the amount of specularity based on the angle of the light.

Hope this is what you are looking for!



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