The difference between twisting and false twisting
If one end of the spinning is held and the other end is rotated, the yarn is formed. This process is called twisting.
Twisting design affects the physical and mechanical properties and appearance of tow, yarn and thread, and then has a great impact on fabric properties, appearance and use value.
For short fiber yarns, twisting is a necessary means for yarn strength and other properties; for filament yarns and ply yarns, twisting can form a compact structure that is not easily damaged by lateral forces. Twisting can also form textured yarn and fancy yarn. The amount and direction of twisting not only affect the handle and appearance of the fabric, but also affect the internal quality of the fabric.
Hold the two ends of the multifilament and twist it through the twisting device in the middle of the two ends of the multifilament. The twist diagram with opposite twist direction and the same number is obtained at the two ends of the twisting device: one end is S-twist, the other is Z-twist. The total twist of the whole yarn is 0.
Generally speaking, the two ends of a rope are fixed and twisted in the middle. The more twisted one side is, the tighter it is. Although the other side is also twisted, the twisting direction is opposite. Therefore, the total number of twists on the rope remains unchanged and is still 0. Therefore, the added twist is called false twist.
source: 123 yarn website