The fresnel node is a single node containing fresnel_blend + reflect + refract. It's no different than my basic fresnel shader that you inserted it into. The reason I don't use the fresnel node is that since it is all of one piece, I cannot control the refraction color nor independently adjust the reflection IOR and the refraction IOR.

What you have done is pretty much equivalent to inserting a copy of my fresnel shader into my fresnel shader.

What's really going on here is the Glossy node you added. It's firing up the back cloth. The refraction of it is certainly an effect but not getting you closer to realism. Cloth doesn't refract. It has tiny holes (pretty much tunnels) and it has thickness (the tunnels have a depth). When these tunnels line up right, you can see through them. At other times the light bounces around and lights the walls of those tunnels, and if the angle is right you can see those lit walls.

 

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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)