Polyethylene terephthalate film

An article of manufacture suitable for use in optically transparent glass laminar structures comprising a frangible, dimensionally stabilized and optically transparent film structure of crystalline polyethylene terephthalate which is asymmetrically oriented by stretching 1.0 to 1.25 times in one direction in the plane of the film and about from 3 to 4 times in a second direction in the plane of the film, the film having a pneumatic impact strength of less than 10 kg.-cm., a tensile strength at break of less than 12,000 psi in at least one direction of said film and an elongation at break of less than 50% in the same film direction, a shrinkage of less than 5% in any direction at 135.degree. C., an optical retardation of about from 5,000 to 7,000 millimicrons, a thickness of at least 1 mil and a gauge deviation of less than 1% per inch along the surface of said film, wherein said film structure is substantially free of color fringes upon viewing in partially polarized light.