The Lee Filters 3x3" 81B Color Conversion Polyester Filter controls the bluish coloration that can affect daylight film. This filter gives warm scenes shot on cloudy days. This filter can also remove excessive blue from the effects of electronic flash. This 81B color conversion polyester filter is also good for general scenics when the photographer wishes to remove the bluish cast from open shade or just add warmth to the photograph. The Lee Filters resin filter is made from lightweight, optical polymeric materials.