VRayVolumeGrid is a special kind of volumetric effect that works with grid-based cache formats. Compare with Environment Fog which is a general purpose volumetric effect. The Volumetric Grid reads its data from an input file which supports grid-based representation of the volume.
Currently VRayVolumeGrid supports three volume formats:
Fancy Bullets
type
circle
OpenVDB (.vdb) - Supported by Houdini ®, FumeFX ® and RealFlow ®
Field3D (.f3d) - Supported FumeFX ® and Maya ® (using 3rd party plugins)
PhoenixFD (.aur) - Phoenix FD ® native volume format
Immediately after the VRayVolumeGrid node is created, a properties dialog appears with a field for selecting the input file. A number of options are then available to fine-tune and customize the volume.