The composition, properties and construction of a backsheet have a direct bearing on its functional performance in a photovoltaic module. Typically, the performance properties are examined under fixed stress conditions and the performance and stability of backsheets to these stress conditions are studied. But exposure to the outdoor environment involves stresses acting sequentially and simultaneously. The effect of these stresses should be applied to modules as well as components to adequately assess their impact on performance and durability. To better understand the expected performance in the field, we have examined established and new backsheet constructions and characterized their initial properties and durability under the usual accelerated test stressors (heat, humidity, UV, temperature cycling) and under conditions where these stressors are applied sequentially or simultaneously. We have also investigated performance of materials under new stress conditions designed to better simulate the operation of a PV module in the outdoor environment. We have applied weathering conditions based on the expected life of the product under various climates to temperature and UV exposure using albedo exposure from the back of the module and using transmitted UV light through the package. The performance and durability of modules from the field after long outdoor exposure are further examined by non-destructive and destructive analysis. Backsheet constructions are identified and module performance is assessed using IV, EL, insulation, color, visual assessment, and ATR-IR spectroscopy. Further assessment employing sampling techniques and a wide range of analytical methods to better understand chemical and physical changes is also described.