in the production of polyester fibers in a melt - spinning process , the transfer system between the melt source and the spinning position has a special importance due to the thermal degradation of the polyester . the present invention provides an improved transfer process which ensures relatively low thermal degradation of the molten polymer . the process is characterized by employment of two or more indexes whereby transfer elements and polymer flows in the transfer system may be correlated for minimum degradation of the polymer . the invention is of particular importance in a continuous process involving continuous polyester polycondensation coupled with continuous melt - spinning .