I wanted Plexiglas because the poly(methyl methacrylate) is transparent to UV radiation - that is, the UV passes thru the acrylic without stopping and doing consequent damage. Not so with the polycarbonate - it is opaque to UV, meaning it absorbs it and suffers the consequences.
Amazingly, the shower curtains have about the same transparency as the aged Lexan, and are not brown - they are actually an improvement. But we do feel like we are outside - the shower curtains do nothing to stop the outside sounds from coming in. The birds are especially entertaining at first light.
I desperately hope we can get the materials in, the windows reglazed and reinstalled before the fall rains begin in earnest.