Use the VRayMtl whenever possible in your scenes. This material is specifically optimized for V-Ray and often GI and lighting is computed much faster for V-Ray materials than for standard 3ds Max materials. Many V-Ray features (e.g. Light Cache, render elements) are guaranteed to work properly only with VRayMtl and other V-Ray compliant materials.
VRayMtl can produce reflections/refractions for matte objects – see VRayMtlWrapper.
There's currently a known issue with setting the Opacity mode to Clip and bump mapping not rendering properly on a material. A workaround is to load the opacity map through a VRayBitmap texture map.
Note that Sheen, Coat and Reflection components are affected by the following parameters: Use roughness, Trace Reflections, Max Depth, Dim Distance, Dim Falloff, Reflect on Back Side, Affect Channels.
