In film blowing, flow instabilities limit the production rate and the quality of the film produced. The phenomena of sharkskin and melt fracture are known to commence when a critical wall shear stress is exceeded at the die lips. The critical value from laboratory experiments with capillaries is usually reported as 0.14 MPa, while in industrial installations much higher values are attained with the use of various additives, such as fluorocarbon polymers for LLDPE. In other processes involving polymer melt stretching, such as melt spinning and film casting, the phenomenon of draw resonance might be present under certain conditions. Draw resonance is a periodic fluctuation of diameter (in me