Yarn is divided into short fiber yarn, by short fibers (natural short fiber or fiber cut fibre) through spinning processing into, dividing ring yarn, free end spinning, yarn from the twist. ② continuous filament, such as natural silk and chemical fiber filament, divided into or not add twist, smooth filament or deformed filament and so on. ③ short fiber and continuous filament yarn, such as polyester cotton filament core yarn. The line is made by two or more single yarn and combined with a twist.
The fineness of the yarn has a variety of representations, such as number, metric, inch, Neil, etc. (see number of branches). The twist of the yarn is expressed in the number of each metre or per inch. The direction of the return is divided by S and Z Twist. In a certain degree of range, the intensity of the yarn increases with the increase of the degree of twist. The twist and alignment collocation of single yarn is chosen according to the use of the strands. Usually the single-yarn and the strands of the contrary to the twist, namely ZS or SZ. Single yarn and strands of the twist has a best ratio, in this range, the strands of strength along with the increase of the strands of the line, more than the critical value of the strength of the line decreases.