We may be at cross-purposes here, but real double sided polygons should be avoided when making stuff for Poser. They will cause all sorts of horrible artifacts when rendering, and also probably choke the cloth room. As Mark says, there are techniques for rendering the "inside" of polygons. If you do need to model the inside of a mesh, for example to get a lining inside a coat or something like that, you should give it some thickness to avoid the rendering problems. It won't work very well in the cloth room, though.