Polymesh rendered as a volume (rollover image).
noise connected (through range shader) to displacement of standard_volume.
step_size: 0.1, volume_padding: 0.05.
When the Step Size is positive, it turns a polymesh into a volume and its value is used as the base step for raymarching the volume.
The mesh should be closed and not have anything self-intersecting, otherwise, the volume may not render correctly.
You must add a step_size value and assign a standard_volume shader for the mesh to render as a volume.
A tutorial that covers how to render a polymesh as a volume can be found here.
More information about volume step_size can be found here.
Head models rendered as volumes with different textures connected to displacement of standard_volume
Pepe model by Daniel M. Lara (Pepeland)