This report has been commissioned by the Swedish Environmental Protection Agency (Naturvårdsverket) with the aim to investigate the potential influence of yarn construction on the fragmentation of microplastic fibres (MPF) in textile fabrics. The analyses were conducted on multiple fabrics with identical constructions but utilizing different types of yarn, such as spun yarn and filament yarn. These fabrics underwent various test simulating the wear experienced throughout a fabric’s lifecycle, including washing, abrasion, and pilling. The research findings highlight the significant influence of yarn type on shedding behaviour. Specifically, spun yarn demonstrates a heightened propensity to shed fibre fragments compared to filament yarns, particularly noticeable during flat abrasion test such as pilling and Martindale, as well as during laundry processes. In contrast, regardless of being spun- or filament yarn, viscose yarn demonstrated lower fibre shedding rates compared to polyester yarn. Furthermore, the chemical recycled polyester yarn showed a tendency to shed more fibre fragments than primary polyester yarn. The conclusions drawn from this report underscores the importance of incorporating yarn quality considerations into eco-design requirements, as suggested by the EU Commission, to effectively mitigate environmental impacts. Further research is essential to enhance our understanding of the factors influencing fibre shedding and to develop efficient strategies for sustainable product design and regulation.