what we've used with great success for a interior reflecting materiel is a syrofoam board insulating materiel with a pebble finish mylar foil covering on one side. in a variety of thicknesses (it also holds temps more stable than a plain cabinet wall.) you'll find it at most home centers. its soft , easy to work and best of all shiny and cheap
your shade idea sounds great! although complicated im going to love to see the end result. what level of finish are you contemplating?
best i love this stuff!!
sp