Sunpak's Twin Pack combines the two most popular filters: Ultra Violet & Circular Polarizer.
The Ultra Violet (UV) filter absorbs ultraviolet rays which often makes outdoor photographs hazy and indistinct. A muliti-purpose fine-weather filter for color as well as black and white films, it eliminates haze and serves as a lens protector.
Light rays which are reflected by any surface become polarised. The Circular Polariser filter is used to select which light rays enter your camara lens. They allow you to remove unwanted reflections from non-metallic surfaces such as water, glass etc. They also saturate colors and increase contrast creating dramatic sky/cloud contrast. Increases contrast equally well with black & white film.