Polymers are used in various industrial applications due to their ease of production, light weight and ductility. Fillers such as clays are added to polymers to improve a range of factors such as material processing and cost. However, adding clays may negatively impact the mechanical performance, affecting the strength, stiffness and impact resistance of the composite. In addition, manufacturing parameters (e.g. number of extrusions, press time, sample cooling method) also have an influence on the resulting composite system. This paper analyses previously obtained experimental results on various clay fillers added to high density polyethylene (HDPE). The composite material was compounded using an extrusion process and manufactured into tensile test samples by means of hot pressing. Various manufacturing (number of extrusions, press time, sample cooling method), material (polymer grade, clay type, clay weight loading) and testing (strain rate) parameters were investigated to determine their influence on the mechanical properties of the composite system. The results showed wide variability, necessitating a statistical approach. Exploratory data analysis and statistical analysis techniques are applied to the historical tensile test data to gain insight into the influence, relationships and interactions of the various parameters of interest on the mechanical properties, specifically strength (ultimate tensile strength) and ductility (percentage elongation at failure). The statistical analysis concluded that all parameters, except for press time, have a statistically significant influence on the mechanical properties of interest. This influence was then qualified through the insights of exploratory data analysis, and knowledge of the material and manufacturing process. The conclusions and insights gained from these analyses will be used to inform a statistical design of experiments to explore the manufacturing variability and reliability in a future study.