The present invention relates to a process for minimizing the flow instability of molten plastics caused by slippage of the melt at the die wall during the extrusion process. The slippage, and therefore the flow instability, is minimized by removing the air from, or "degassing", the polymer prior to the extrusion process, preferably by subjecting the molten polymer to a vacuum for an extended time, typically 24 hours. Further, air is preferably prevented from being introduced into the molten polymer, the extrusion die or the extrusion process from the ambient conditions surrounding the extrusion process during the extrusion process by creating a vacuum over the polymer hopper, the feed region of the extrusion system, the exit portion of the die, the entire extrusion system or any combination thereof.