Knitting fly is identified with the impossibility of collection at one location and regular machine cleaning needed to remove it. Fabric defects can occur and it is a health hazard to operatives. Yarn abrasion and amount of fluff liberated depend on wrap of the yarn around different guides, yarn-input tension, coefficient of friction between yarn and contact surface, and hairiness and twist factor. These are discussed, with hairiness particularly considered and the use of computer software described. To evaluate the effect of various yarn parameters on knitting fly formation, data was gathered on knitting waste. In practical terms this is expensive so a simulation knitting process was developed and discussed. Six yarns were analysed and are used extensively in Mauritius. Hairiness, friction and amount of fly are covered, with hairiness the dominant factor. The relationship between twist factor and friction with fly formation need further investigation.