A photovoltaic module and its components are exposed to the natural variability of stress factors in outdoor environments. This variable environment makes it difficult to choose an adequate backsheet for each field operating conditions. To account for these factors, we investigate the mechanism of degradation for several types of backsheets which were aged under different levels of damp heat as well as pressure cooker test. The study quantitatively demonstrates how environmental stresses impact the degradation in performance of different types of backsheets. The degradation of backsheet was quantitatively investigated by mechanical tensile. To describe the degradation mechanism, the molecular weight of core materials was measured by using gel permeation chromatography. An accelerated test conditions resulted in significant hydrolysis of core materials and degrease in molecular weight of them. Tests show the degradation pattern of different types of backsheets for each accelerated test conditions. In addition, the degradation pattern aged under damp heat and pressure cooker test can be correlated and the latter can provide rapid material evaluation. (C) 2013 Elsevier B.V. All rights reserved.