Does the circular polarizer material have to face a particular direction?

The linear polarizing side of the circular polarizer must face the observer. In this alignment, randomly polarized ambient light will be linearly polarized before it passes through the retarder side of the film and becomes circularly polarized. A quick test for orientation is to place a mirror behind the circular polarizer with a light source on the opposite viewing side. Upon reflection, the circularly polarized light is blocked from reaching the observer (in the form of glare). When the orientation is correct, the light reflecting from the mirror should not be visible. Randomly polarized light from the non-viewing side of the polarizer is allowed to pass through the material.