Flipping faces in a material, possible?

Is it possible to flip faces on a mesh in a material? I’d like to make a single sided material capable of turning a piece of geometry inside out. I can invert the surface normals, but the face orientation I guess is defined by the winding order of the vertices; so on a sphere for example, the lighting is flipped but the surface still faces outwards. I could flip the faces in a modeling package but I’d really like to do this in a material. Is it possible?

If you don’t care about performance you could try the following: make your material masked and two sided and use the two-sided sign node to mask either the front or back facing triangles.

This should give you the result you are after, but will be a bit more expensive to render as you are effectively rendering both sides, even though you only see one.


That’s clever, but yes performance is a concern. I will give it a go, but definitely interested in other ideas people may have.