Light rays which are reflected by any surface become polarized and polarizing filters are used to select which light rays enter your camara lens. PL-CIR (Circular Polarizing) filters allow you to remove unwanted reflections from non-metallic surfaces such as water, glass etc. They also enable colors to become more saturated and appear clearer, with better contrast. This effect is often used to increase the contrast and saturation in blue skies and white clouds. HOYA's polarising filters do not affect the overall color balance of a shot.