This page provides information about the Material from File in V-Ray for Grasshopper.
Overview
V-Ray Material from File loads a .vrmat file. Click on the field to open a file browser window and select a .vrmat file.
Right-click on the node to open V-Ray Material from File context menu.
The Library Materials command allows you to load any of the built-in material files from the V-Ray preset material library. Note that this command does not allow loading materials from custom locations added to the Asset Editor's Material Library panel..
Note that invalid input file paths are auto-resolved as long as the files reside at the same location as the .gh project file
Usage Example
Vertex Color Setup. Note the UVW texture is set to UV channel 2
Matching Grasshopper vertex color data between the Rhino Viewport and the VFB