Hoya 37mm HD2 Protector, 8-layer Multi-Coated Glass Filter

Light rays which are reflected by any surface become polarised and polarising filters are used to select which light rays enter your camera lens.
@@ They allow you to remove unwanted reflections from non-metallic surfaces such as water, glass etc.
@@ They also saturate colors and increase contrast.
@@Polarizers come in two variations but have the same effect. Linear polarizers work with older camera meters; Circurlar polarizers are designed for today's newer split-beam metering systems used in auto focus cameras. Check your camera's manual.