This page gives some basic details about the Reflection Glossiness render element and how it is used in compositing.
||Render Setup window|| > Render Elements tab > Add button > VRayMtlReflectGlossiness
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.
This render element can be baked to a texture for use within a real-time engine.
Select the appropriate Width and Height. Under Mapping Coordinates be sure to select Use Existing Channel if the object already has UV Mapping applied.
Select the three dots next to File Name and Type to select an output location before clicking Render to begin baking.
Import the maps into a real-time engine. The following example is Unreal Engine 4.