In fact, flat hard transparent CD/DVD plastic packages are made of polycarbonate (guess);
Hi Doron, I think they are Polystyrene, cheap and transparent.
Bob, thanks for the correction; yes it is polystyrene.
Just for fun, I performed a small experiment with cellophane and a CD package plate. Such experiments have been done and posted by other folks in the past.
1) Sandwiched A 2cm x 2cm piece of thin flower-wrap cellophane
between twp slides, placed the sandwich-slide on top of the polarizer (which in turn is laid on the field aperture). The other polarizer in inside the head, above the objectives. Rotation of the sandwich-slide creates a partial spectrum of background colors. Adding a second layer of cellophane creates a full spectrum and fairly strong coloration.
2) Cut a 2cm X 2cm piece of solid transparent polystyrene from the front plate of a DVD package
. Placed the piece on the polarizer on top of the field aperture, and repeated the experiment. The same rainbow effect was obtained. I was not sure about the birefringence of PS, but there it is and it works.