The opacity of the front surface. A value of 0% allows for no diffuse color or surface to show through (unless Roughness Intensity is not equal to zero). Values greater than zero allow the surface color to show through (which is the diffuse color).
The back surface opacity. The back surface works the same as the front surface opacity. Keep in mind that the back surface is affected by shadows also.
This causes the edges of an object that points further away from the camera to be more opaque. 0% creates no effect while values greater than zero add to the edge opacity.
The refractive index for the material.
Allows refracted rays to reflect when appropriate.
Makes the object a completely dense object instead of one surface. Disallows illumination, reflection, and environment to be evaluated for the second surface intercepted of the object.