These volume components are designed for use with the material components for refraction/transparency - Beckmann BTDF, GGX BTDF and Specular BTDF.
Exactly the same Transmittance as in the Dielectric material.
The transmittance of a material is its effectiveness in transmitting light - how transparent it is - and what color light it transmits through the material it is paired with.
Transmittance Distance (Scalar)
This is the distance at which the medium absorption color reaches Transmittance Color.
Transmittance requires Volumetrics to be enabled; otherwise, there will be no color.
Volumetric works in the same way as the Sigma 2 material.
Scattering is a volumetric effect. To work properly, it needs to have Affect Volumetrics turned on in lights. Otherwise, it only absorbs light according to the scattering color.
How quickly light passing inside an object is extinguished. A low value here with indicate greater transparency. Based on Beer’s law of absorption, to give a more realistic and non-linear result.
Scales the Scattering and Absorption values.
Ratio between the amount of forward to backward scattering. With a positive value, more light is scattered from behind the object, with a negative value more light is scattered from in front of the object, relative to the observer.
With this example we have two lights, one in front, one behind our sphere. Both are very strong and the one behind is colored green, the one in front red. With Asymmetry set to 0.5, the light from the green light is scattered forward towards the observer, in this case the camera. When Asymmetry is set to -0.5 the light from the red light behind the camera is reflected toward the observer.
Step Size (Scalar)
This is the volumetric scale for your surface. Larger numbers will render faster but be less defined.