The objective of this work is to present a comparative study of the behaviour of a polymer composite before and after accelerated ageing with exposure to UVB radiation and water vapour. The goal is to propose a methodology to characterise material ageing by observing its phenomenological behaviour without taking into account chemical or physical changes that result from ageing. With this objective, tensile and creep tests were performed and the experimental results were used in an inverse approach to identify the material parameters in a three-parameter rheological model. A silica-polytetrafluoroethylene (PTFE) matrix reinforced composite was investigated. It was verified that significant differences in the composite behaviour only occurred after a long time. In particular, the strength of the composite increased significantly.