The twist direction of pure cotton sewing thread is determined by the inclination of twisting fibers in yarn or single yarn in the strands. There are two kinds of Z twist and S twist. The direction of inclination of the fiber or single yarn is from bottom to top, from right to left, called Z twist, also known as backhand twist. The slant direction of fiber or single yarn is called S twist from bottom to top from right to left, also known as "Shun hand twist". The importance of twist lies in the coordination of yarn and yarn twisting and the twist of warp and weft in fabric.
In most cases, the single yarn is twisted by Z, and the strand is twisted with S, which is opposite to each other. The direction of the fiber arrangement is parallel to the strand axis, so the strand is soft and the luster is good, and the twisting and structure are stable. The twist direction of the strand is in the order of twisting and twisting, and it is represented by Z and S at a time. The twisting direction of each strand has great influence on the physical properties of the strand.