OSPRAY Material with extrusion surface

Hello,
I have a 2D surface mesh, and for my visualizations I usually use the “surface extrusion” representation.
I would now like to use better render and therefore use materials with OSPRAY. But it seems that it only works on the “surface” representations. Is it normal ?

If yes, what would you advise to do for an extruded visualization with a material?

Thanks in advance