Microplastics are a pressing global concern. Inhalation of microplastic fibers has been associated with interstitial lung disease related to alveolar epithelial damage in nylon flock workers. However, the means by which fibers affect lung tissue and epithelial growth remains unknown. Our aim was to assess the effects of nylon and polyester textile microplastic fibers on epithelial growth and differentiation using airway and alveolar lung organoids cultured from epithelial cell progenitors, isolated both from murine lungs and human lung tissue obtained from COPD patients. Exposure to nylon (11x30 µm) or polyester (15x53 µm) microfibers resulted in significantly fewer and smaller human and murine airway organoids after 14 days of culture, the effect being most profound with nylon. Alveolar organoids were not affected by these fibers. Incubation with nylon- or polyester-conditioned medium also resulted in fewer airway organoids. Effects were mainly observed in developing airway organoids; exposure of developed organoids from day 14 to day 21 to fibers or fiber-conditioned medium had no significant effect on organoid number or size. In conclusion, airway organoid formation is negatively impacted by the presence of textile microplastic fibers and this effect appears to be mediated by leaching additives. Our results suggest that microplastic fibers may especially harm the developing airways or airways undergoing repair. Further studies will focus on identifying these additives and the mechanism behind their effect. Importantly, wider investigations into the presence of microplastic fibers in human lung tissue are urgently needed to determine the actual risk of these fibers to human health.