This page gives detail about the Refraction Glossiness Color Channel.
Overview
The Refraction Glossiness Render Channel stores the image's refraction glossiness as a grayscale image that represents the degree of Refraction Glossiness set for materials in the scene. White areas have the most refraction glossiness, while dark areas have little.
The amount of refraction glossiness for a material is set by its Refraction Glossiness parameter. For example, V-Ray Material has a Refraction Glossiness parameter, and Skin Material has parameters for primary and secondary refraction glossiness.
UI Path
||Node Editor|| > Add > Render Channels > Color Channel > Type > Refraction Glossiness
