The modeling of the relationship between the extrusion temperature profile and the polymer grade as well as the overall orientation of as-spun aliphatic aromatic copolyester (AAC) fibers has been proposed. Depending on rheological results, AAC fibers were spun. In terms of the extrusion temperature profile and polymer grade, an appropriate statistical analysis of the optical anisotropy of the as-spun fibers was carried out. For measuring the fiber birefringence (optical anisotropy), an interferometric technique was employed. The interest of factorial design is in the restricted numbers of runs, 16 runs for a factorial design at 2 levels with 4 factors, and in the description of rheological mechanisms through mathematical interactions. The results obtained from the melt flow indexer give an explanation for the character of rheological properties and surface shape at different temperatures and loads at which recent analysis was performed. The overall orientation of the spun filaments has been modeled. The model allows a fast simulation to describe the behavior of factors-response relationship. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 1270-1277, 2010