The Refraction Filter Render Channel is an image that stores refraction information calculated from the materials' refraction values in the scene. Materials with no refraction values appear as black, while completely refractive materials appear as white, and everything in between appears as a shade of gray. If any hue (color) is specified in the material's Refractive Color parameter, that hue and value are represented here in the Refraction Filter as well as being affected by the refraction's Amount parameter.

In comparison, the Raw Refraction Render Channel is a color render channel that takes materials and their colors into account when rendering refraction. Multiplying these two render channels together produces the Refraction Render Channel.

Note: To properly calculate the Refraction Filter Render Channel, the Refraction Render Channel must also be added to the list of render channels being calculated during the rendering process to properly determine all the refraction information in the scene.

UI Path: ||V-Ray Node Editor|| > World > Render Channels > Advanced > V-Ray  Refraction Filter

See the Render Channels page to find out where you can find these properties.

Channel Name – Customizable name for the render channel.

Enable Deep Output – Specifies whether to include this render channel in deep images.

Color Mapping – 

Consider For Anti-Aliasing – When enabled, anti-aliasing is used where possible.

Filtering –  Applies an image filter to this channel.

Vfb Color Corrections – Applies the post-render color adjustments made from the VFB.

Denoise – Enables the render channel's denoising, provided the Denoiser is enabled.