: The main purpose of this research work was to illustrate the extent of hydrolytic degradation of PET caused by warm water and also to separate the influence of moisture, temperature and orientation in the degradation process. To achieve this purpose thermal and hydrolytic degradation of PET(chips, POY, FDY) at temperatures above and bellow T g were carried out using a water bath and an electrical oven. Technical methods such as moisture content, densitometery, viscometric analysis, titration, FTIR and x-ray diffraction were used to analyse the degradation PET. The results obtained from different analysis show that the main cause of degradation is carried out by moisture and heat on its own has a minor effect. Degradation at lower temperatures were less prominent and was increased noticeably above T g . Crystallinity plays a significant role in preventing hydrolytic degradation as the extent of degradation was increased from FDY to chips to POY. X-ray diffraction analysis showed that crystallinity was increased from POY to chips to FDY. Determination of intrinsic viscosity, molecular weight based on viscosity(M v ), molecular weight based on weight(M w ), molecular weight based on number(M n ), chain scissions and end group analysis were the main quantities for the degradation measurement.
