Microplastic pollution is everywhere in our oceans and the textile industry has responsibilities in this crisis. In fact, fibre fragmentation of our garments due to abrasion releases microplastics fibres MPF in wastewater during washing. The amount and the weight of MPF is depending on the washing parameters but also on the textile structure itself, and filaments may have a role in this environmental problem. That is why this study looks at the influence of several melt spinning process factors on the MPF release during washing, through a design of experiments DOE with the Taguchi methodology. This DOE is focused on polyester which can be virgin or recycled, with additives like titanium dioxide and dope dye or not, but also with variation in the number of filaments inside the multifilament and in the intermingling frequency. 16 filaments obtained from the DOE are next knitted identically to be tested with the TMC test method to quantify the microplastics fibres release after one washing cycle. Concretely, this work aims to disseminate the results of this study to show how the design of our garments can impact the microplastics release and indeed its environmental footprint directly at the filament manufacturing stage. This study is part of a global thesis led by PhD student textile engineer Antoine Cosne and technical leader textile engineer Marie Stephan from DECATHLON, Pr. Nemeshwaree Massika Behary thesis director and Pr. Anne Perwuelz thesis co-director from GEMTEX laboratory in France, with multifilaments supplier ANTEX in Spain and knits supplier SAMPAIO in Portugal, and financed in part by French supports ADEME and ANRT.