The Sheen Reflection Render Element stores the indirect reflection information calculated from the VRayMtl Sheen Layer. Surfaces Surfaces with no Sheen values set in their materials will contain no information in the render pass and will therefore render black.
The Sheen Reflection Render Element is formed can be obtained by multiplying the Raw Sheen ReflectionRender Element by by the Sheen FilterRender Element. So while the raw sheen reflection pass gives the full reflection of objects reflecting in the scene, the sheen reflection filter sets how much of that reflection should come through in the composite. The two are multiplied together to create the Sheen Reflection pass which gives a true representation of the reflection in the scene.
To use render elements, select from the Available render elements column and click the Add button to add the passes you wish to generate at render time. When you render the scene, the added render elements listed in the column on the right, will also render, which can be viewed from the VFB window's channel drop-down menu.
For more information on the parameters on this dialog, see the Render Elements tab page.
