Textile fibres are derived from natural and artificial fibres and, in some cases, are blended together to ensure optimum properties. Textiles made from cotton and polyester blends currently hold a significant market share as they are relatively inexpensive, offer excellent performance, and have complementary properties. However, the production and consumption of textiles contribute significantly to environmental degradation and greenhouse gas emissions, but the scale of the impact is uncertain and under debate. This is also the case in studies of cotton and polyester blends, as a detailed life cycle inventory of the production of this material is absent in the scientific literature, thus affecting its environmental impact assessment. Therefore, the study aimed to identify the limitations and assumptions used so far in the environmental assessments of cotton and polyester blends and to assess the uncertainties they may introduce in future environmental assessments. Two methods were used: literature analysis and scenario-based life cycle assessment. The literature analysis summarized five studies and reports that have carried out an environmental assessment of blended textiles and provided inventory data. The results of the life cycle assessment showed that it is not possible to fill the knowledge gap by creating a new life cycle inventory using existing literature data. This is because the uncertainty in results was too high, reaching as much as 772 % difference from the baseline scenario. Nevertheless, this study is a step towards a complete life cycle inventory and can improve the future environmental assessment of textile blends.