This article investigates how the bending stiffness of the core thread and the effect threads affect the average values and the variability of the structural properties of resultant fancy yarns. The Design of Experiment technique was used to study the effects of individual factors and the interactions of factors. The analysis indicated that that the bending stiffness of the effect thread was a main factor. Increases in the effect thread bending stiffness led to significant increases of the size of fancy profile and reductions of the number of fancy
profiles. Further, there was a strong interaction effect between the bending stiffness of the core thread and the bending stiffness of the effect thread that influenced the structures of the resultant fancy yarns. It was also found that variations in the bending stiffness of the input threads were reflected in similar variations in the size and number of fancy profiles. The study is important for engineering the structure and the variation in structural properties of fancy
yarns by selecting appropriate input threads.