This paper presents an optical microstructural model showing, the behavior of blown low-density polyethylene films as optical polymers (birefringence and anisotropy), at a structural level. The model is mainly based on a microstructural study involving the observation and analysis of increasingly smaller structures by transmission electron microscopy, POM, and X-ray diffraction, as a means of calculating the values of their orientation functions (the uniaxial approximation). These values enabled us to indicate graphically the most probable average position of the unit cell (the natural scale of our model) and hence of other crystalline structures. (C) 2000 John Wiley & Sons, Inc.