In the discussion of materials and front- and back-face orientation of polygons, we have already touched on some limitations you may encounter when using external renderers. SketchUp is designed for quick and sketchy projects and uses OpenGL for its visuals. Photorealistic renderers use a number of techniques that have other requirements for their input.
The following are some of the most common conflicts between SketchUp and third-party renderers that you should look out for when preparing scenes for export:
Polygon orientation: As mentioned earlier, not all renderers can handle the display of back-facing polygons. Even if they are able to render the reverse side of a face, it will certainly cause issues when you assign an emitting material to the face to simulate light. Verify the orientation of all polygons in your model before you export.
Two-sided polygons: SketchUp can assign different materials to the front and the back of a polygon. This is not...