You can use regular food wrap foil with the shiny side up too. He just got the decorating stuff because it was on sale. You can also get thin sheets of mirrored plastic and arch it in there. Watch out for the mylar stuff, it conducts electricity. Combined with salt water and electric lights, well you get the idea. I knew another guy that used some mirrored contact paper that people used to put up in their rec rooms in the 80's. It ended up in a big sticky mess.