Moisture ingress and thermal effects on carbon fibre reinforced plastic is a well understood phenomenon. For aircraft structures where safety is paramount this results in the use of worst case material properties, known as HOTAA/ET properties. In reality most structures are not fully saturated and are therefore penalised by using these worst case properties. This project attempts to fully understand the environmental effect on mechanical performance and accurately model a structures exposure to the environment, while still maintaining conservatism, to realise structural weight savings for aircraft. From the literature study it appears that this is the first attempt to link the mechanical property degradation brought about by environment, to classical laminate theory. By modelling individual ply property performance, based on each ply's level of saturation and linking it to a bespoke set of materials properties generated within the project, it is possible to accurately model the mechanical performance of a component. The model and modelling process derived within this project have been successfully validated by structural testing.