Product quality and, in general, processing windows and rates of production in the extrusion of molten polymers are limited by various flow instabilities (mainly melt fracture) that are observed at high production rates. While there still are unresolved issues in comprehending these phenomena, industry demands for process optimization dictate the employment of processing aids for product quality improvement and energy requirement reduction. In this review paper, most commercially used processing aids are discussed, the purpose of this work is to investigate the effect of Boron- nitride,Nano-clay and Fluoropolymer PPA on the polypropylene (PP) flow instabilities. In this work, the Capillary rheometer is used in order to simulate the flow behavior and to determine the shear rate at which smooth extrudates can be produced. Moreover, the Parallel-plate rheometer is used in order to study of the effect of PPAs on the linear viscoelastic behavior of the PP. The results indicate that using the combination of PPAs reduces the flow instabilities more effectively and improve the extrusion process.