This filter is for black and white infrared film when you only want to transmit the infrared spectrum and none of the visible spectrum. Filter factor is determined by the film sensitivity.
Lee gelatin filters are available in 3 x 3" (75 x 75mm), 4 x 4" (100 x 100mm)
Reviews LEE Filters 3x3" Infra Red #87 Infrared Polyester Filter