This page gives some basic details about the Refraction Glossiness Render Element.
The Refraction Glossiness Render Element stores refraction information set in a V-Ray material's refraction Glossiness value in the scene. Materials with no refraction values appear as white, while refractive materials represent the value set in the Refraction Glossiness parameter of that material.
Note: To correctly calculate the Refraction Filter Render Element, the Refraction Render Element must also be added to the list of render elements being calculated during the rendering process to properly determine all the refraction information in the scene.
This render element is enabled through the Render Elements tab of the Render Setup window in 3ds Max and displays its parameters in a rollout at the bottom of the window:
VRayVFB – When enabled, the render element appears in the V-Ray Virtual Frame Buffer.
Deep output – Specifies whether to include this render element in deep images.