This article is a discussion of Cronar polyester photographic film base. The basic raw materials which make it up are: dimethyl terephthalate and ethylene glycol. Its properties include optical clarity, high wear and tear resistance, low moisture sensitivity, relatively high stiffness modulus. It can be used with less thickness than cellulose triacetate. There are several tables which compare the properties of these two supports. The chemical inertness of Cronar is favorable for obtaining desirable ageing characteristics of finished films. The article describes the tests and standards applied to this film which offers substantial savings in weight and space.