Lets you simulate a Fresnel reflection (internally, nothing is actually reflected), i.e., on surfaces that lie at acute angles to the camera’s angle of view will be darkened and contours will be made somewhat more prominent. This is especially useful for reflective materials such as ice or polished jade. Often, however, it is quite irritating, in which case the value should be left at 0.
Often when using fine color gradients a banding effect - color stepping - occurs. Dithering applies a more-or-less subtle Noise, which can eliminate these steps. Values greater than 100% can be used!
This setting defines a refraction index with regard to the SSS effect. The result: the greater the value, the darker the SSS. Normally, however, you should not have to modify this value.