The Polygon Side texture map renders white on the front face and black on the backface of a polygon. You can use this for backface culling by putting this texture into the Opacity channel. You can also use this to allow double-sided materials by placing it into a Mix material, and double-sided textures by placing it into a Mix texture (figure 1). In the following illustration, the NodeGraph Editor window is used to clearly illustrate the association of the various texture nodes.
Figure 3: A twisted surface with a red texture mapped to one side of the polygon and a blue texture mapped to the other.