The Reflection Render Element stores reflection information calculated from the materials' reflection values in the scene. Surfaces with no reflection values set in their materials will contain no information in the render pass and will therefore render as black.
The Reflection Render Element is formed by multiplying the Raw Reflection (vrayRE_Raw_Reflection) Render Element by the Reflection Filter (vrayRE_Reflection_Filter) Render Element . So while the raw reflection pass gives the full reflection of objects reflecting in the scene, the reflection filter sets how much of that reflection should come through in the composite. The two are multiplied together to create the vrayRE_Reflection pass which gives a true representation of the reflection in the scene.
The Reflection Render Element is a key component in the main Beauty Pass.
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.
