Well, I had always pictured a gloss white (trim or exterior) rather than a flat white (ceiling) as the better reflector. I always think of blinding myself looking at a freshly-painted building on a sunny day. I guess in this case, if the OP was to not use the PVC, painting might be more effective (more spread?), and if he were to use the PVC, foil maybe.
Am I correct in remembering that the dull vs. shiny side of aluminum wasn't different enough to worry about?