Polypropylene frosted sheet.
These sheets have a frosted / transluscent appearence - matt on one side, satin on other and are very popular material for making covers for brochures, folders etc.
Can also be used to represent water surface, maybe layered with illusion film (JAWS).
Polypropylene frosted sheets can be used for creating lamp shades, although care should be taken that there is enough distance between the film and the light (heat) source because polypropylene`s heat-resistance is not unlimited.