Atmospheric microplastics have been widely reported in studies around the world. Microfibres are often the dominant morphology found by researchers, although synthetic (i.e., plastic) microfibres are typically just a fraction of the total number of microfibres, with other, non-synthetic, cellulosic microfibres frequently being reported. This study set out to review existing literature to determine the relative proportion of cellulosic and synthetic atmospheric anthropogenic (man-made) microfibres, discuss trends in the microfibre abundances, and outline proposed best-practices for future studies. We conducted a systematic review of the existing literature and identified 33 peer-reviewed articles from Scopus and Google Scholar searches that examined cellulosic microfibres and synthetic microfibres in the atmosphere. Multiple analyses indicate that cellulosic microfibres are considerably more common than synthetic microfibres. FT-IR and Raman spectroscopy data obtained from 24 studies, showed that 57% of microfibres were cellulosic and 23% were synthetic. The remaining were either inorganic, or not determined. In total, 20 studies identified more cellulosic microfibres, compared to 11 studies which identified more synthetic microfibres. The data show that cellulosic microfibres are 2.5 times more abundant between 2016 and 2022, however, the proportion of cellulosic microfibres appear to be decreasing, while synthetic microfibres are increasing. We expect a crossover to happen by 2030, where synthetic microfibres will be dominant in the atmosphere. We propose that future studies on atmospheric anthropogenic microfibres should include information on natural and regenerated cellulosic microfibres, and design studies which are inclusive of cellulosic microfibres during analysis and reporting. This will allow researchers to monitor trends in the composition of atmospheric microfibers and will help address the frequent underestimation of cellulosic microfibre abundance in the atmosphere.