Abstract: An optically virtually isotropic plastic film, in particular for use in liquid crystal displays, can be produced by a method in which first an optically uniaxial birefringent plastic film is produced by casting or extrusion, and then irreversible molecular reorientation is produced in layers of the film close to the surface by heating or by immersion in a solvent or swelling agent. This reoriented structure is retained after cooling or drying of the film, and results in the birefringence (anisotropy) initially present being eliminated or compensated.

Abstract: Birefringence-free arrangement of plastic foils, characterized in that two plastic foils having a single principal optical axis, said optical axis lying within the plane of the plastic foil, are arranged parallel behind each other so that the optical axes of both plastic foils are forming an angle of 90.degree..+-.7.degree. and the material of the foils with regard to its optical properties and the thickness of the foils being selected in such a manner that the optical path differences .DELTA.n.sub.1 D.sub.1 for the light waves which are associated with the two main refraction indices within the first plastic foil is approximately equal to the optical path difference .DELTA.n.sub.2 d.sub.2 of the second plastic foil, .DELTA.n.sub.1, .DELTA.n.sub.2, being the difference of the main refraction indices in the first and second foil, respectively, and d.sub.1, d.sub.