This paper analyzes the impact of knitwear’s fiber composition, linear density and finishing of yarn used in the dimensional stability of the 1x1 RIB knitwear made on the same circular knitting machine. Dimensional stability of these samples was analysed by FAST 4 method. Different samples were compared across multiple indicators. The results show that the most stable dyed knitted fabric are made of cotton 96% and 4% of Lycra and of yarn with linear density 19.14 tex. Tightness factor’s values in the dry relaxation stood at 17.90, in the wet 18.45, in total 18.73 and 18.59 in air conditioned terms. Knitwear with the highest values of dimensional instability are raw knitted fabric made of 100% CO, and yarn with linear density of 13.39 tex. Tightness factor’s values in the dry relaxation stood at 12.16, in the wet 12.36, in total 13.26 and 13.35 in air conditioned terms