Purpose – The purpose of the research is to explore how defective parts and products affect the sustainability aspect of manufacturing companies and how defects can be reduced. 

Method – To reach the purpose of the study, a single case study and literature review have been conducted. The single case study has used an abductive approach throughout the study with the use of quantitative and qualitative data. The different methods to collect the data throughout the study were observations, interviews, questionnaires, and document studies. The empirical data was later analysed with pattern matching against the theoretical framework to reach results. 

Findings – It is clear that defective parts and products have a negative effect on manufacturers’ sustainability performance. The use of lean methodology and its tools can provide manufacturing companies with accurate information on what defects they have and the causes behind, in order to reduce the number of defects and improve the sustainability aspect.  

Limitations – The research has been limited to one company and a certain area within its production. The studied area was further narrowed down to only include the closest processes to the machines, hence, processes before and after the area are not covered in this research. 

Keywords – Defects, Sustainability, Production, Lean, Plastic injection moulding, Process.