Background- Polymer Rapid Tooling (PRT) inserts for Injection Moulding (IM) are a cost-effective method for prototyping and low volume manufacturing. However, PRT inserts lack the robustness of steel inserts, leading to progressive deterioration and failure. This causes quality issues and reduced tool life. Approach- Case studies performed on PRT inserts have revealed progressive failures over the life of the tool. Moulded parts were examined to further understand the failures and identify root causes. From this a candidate set-up process was developed to avoid start-up failure and prolong tool life. This process was tested on a second mould, which successfully avoided start up failure and moulded 28 parts before becoming unusable due to safety issues. Findings- Process parameters critical for tool life have been identified as: mould temperature, injection pressure, injection speed, hold pressure, and cooling time. The effect of these parameters on different areas of the tool have been identified. Failure modes have been categorized as: Surface Deterioration; Surface Scalding; Avulsion; Shear Failure; Bending Failure and Edge Failure. These failure modes influence each other and may be connected in cascade sequences. Originality- We have developed a novel method for setting IM process parameters for PRT inserts to prevent failure at start-up and extend operating life. Failure modes and their relationship with root causes have been identified.