The specification of new or enhanced materials is often based on results from simplified injection moulded test specimens produced by idealised melt flow conditions. Design data obtained is then used to predict the mechanical behaviour of a final part, using practical or computational techniques, often without sufficient attention to the change in performance due to differences in flow behaviour when injecting more sophisticated geometries. To overcome this problem without being dependent on a time-consuming prototyping phase, the aim of this investigation is to evaluate a new mould concept which allows controlled modification of the material flow by adding specific mould tool design features which lead to flow hesitation, creation of weld-lines and combinations of each of these irregular flow phenomena. Verification of these effects from practical research based upon polyamides was evaluated by thermal analysis (DSC), whilst optical microscopy was used to highlight microstructural differences of injection moulded test components produced with the concept mould and in more complex products. In parallel, the influence on the mechanical performance was investigated by testing specimens obtained from regions of the concept tool with varying microstructural features, with particular focus on high-velocity impact, tensile and dynamic fatigue properties. Results showed significant changes in impact energy, tensile toughness and fatigue behaviour for the new mould specimens produced at certain locations within the concept mould where flow modifications were evident; similar behaviour is anticipated for finished parts with similar microstructural features. Therefore, this approach narrows the existing knowledge gap by delivering results with a higher practical relevance while still allowing consistent sample preparation to comply with industrial standards. KEYWORDS: Injection moulding / concept mould / microstructure flow hesitation / weld lines