In this work, the Pluta interference microscope was used to study the effect of drawing process on the optical, structural, and mechanical properties of polyethylene terephthalate (PET) fibers. The orientational behavior of drawn PET fibers to different draw ratios was investigated using the calculated values of the refractive indices and the double refraction. Changing the draw ratio resulted in changes in optical parameters, which were used to determine the mechanical factors of orientation. Different orientation functions, such as f2(θ), f4(θ), f6(θ), fa, fc, and fav, were calculated. Molecular reorientation during the cold drawing process can be considered the main reason for the major variations in the properties of PET fibers. It can be concluded that double refraction related to the total overall orientation of the crystalline and amorphous phases. The different crystallinities parameter were measured. the calculated data show that the
dawing process has a great effect on the different properties of the fiber. Microinterferograms were utilized to illustrate these variations.