. "The polymer sheet may vary widely in thickness and may be in itself a self-supporting film or plate, or it can be in the form of a layer of the desired synthetic polymer carried on a suitable support, such as, a film, e.g., a cellulose derivative including cellulose acetate, cellulose propionate, cellulose acetate butyrate, etc.; a super polymer, including nylon, a polyethylene terephthalate, poly" . . . . .