This article illustrates a Six Sigma project aimed at reducing manufacturing-induced visual deviations for fibre-reinforced polymer (FRP) composites. For a European composites manufacturer, such visual deviations lead to scrapping of cylindrical composite bodies and subsequent environmental impact. The composite bodies are manufactured through vacuum infusion, where a resin mixture impregnates a fibreglass preform and cures, transforming from liquid to solid state. We illustrate the define-measure-analyse-improve-control (DMAIC) steps of the Six Sigma project. Specific emphasis is placed on the measure and analyse steps featuring a 36-run computer-generated mixture experiment with six resin mixture components and six responses. Experimental analysis establishes causal relationships between mixture components and correlated resin characteristics, which can be used to control resin characteristics. Two new resin mixtures were developed and tested in the improve step using the understanding developed in previous steps. Manufacturing-induced visual deviations were greatly reduced by adjusting the resin mixture to induce a slower curing process. Further refinement of the mixture was made in the control step. A production scrap rate of 5% due to visual deviations was measured during a monitoring period of 5 months after the resin mixture change. The scrap rate was substantially improved compared to the historical level (60%). The successful experimental investigation integrated in this Six Sigma project is expected to generate increased quality, competitiveness, and substantial savings.