Regarding your question about seeing the back side of a polygon, the answer is yes, but seeing isn't the question. The important question is will it react to light properly. And the answer to that is entirely dependent on whether you're using FireFly vs. SuperFly and whether you have set the shader up properly to treat both sides the same or you have them set to behave differently. There's no right approach here.

For example, the back side of a single-poly flag should look and react to light just like the front side. The back side of a glass fish tank filled with water should not.

Here my box walls are set up to mimic frosted glass. We see the inner or "back" side of the boxes because the shader uses refraction and the Fresnel effect and in fact the back face renders differently than the front. It has to, because it's following the rules of physics, not the rules of 3D model tricks.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)