Yarn is divided into: ①Short fiber yarn, which is made of short fiber (natural staple fiber or chemical fiber cut fiber) by spinning, and is divided into ring-spun yarn, free-end spinning, self-twisting yarn, etc. ②Continuous filaments, such as natural silk and chemical fiber filaments, with or without twisting, smooth filaments or textured filaments, etc. ③ Short fiber and continuous filament combined yarn, such as polyester-cotton filament core-spun yarn, etc. The thread is made of two or more single yarns that are combined and twisted.

There are many ways to express the fineness of yarn, such as number, metric count, imperial count, denier, etc. (see count). Yarn twist is expressed in turns per meter or inch. The direction of twist is divided into S twist and Z twist. Within a certain twist range, the yarn strength increases with the twist. The twist direction of the single yarn and the twist direction of the strands are selected according to the use of the strands. Usually single yarn and strand adopt opposite twist direction, namely ZS or SZ. The twist degree of single yarn and strand has an optimal ratio. Within this range, the strand strength increases with the increase of the twist degree of the strand, and when it exceeds the critical value, the strand strength decreases instead. The properties of the fibers and the spinning method play a decisive role in the properties of the yarn. During the twisting process of ring spun yarn, due to the transfer of fibers, from the inner layer of the yarn to the outer layer, and then from the outer layer to the inner layer, the transfer is repeated many times.

The fibers are spiral around the axis of the yarn, and the spiral radius is along the axis. increase or decrease alternately. At this time, the fibers with long length tend to tend to the axis of the yarn more, and the fibers with short length tend to tend to the outer layer of the yarn. The finer fibers tend to the axis of the yarn, and the coarser fibers tend to the outer layer of the yarn. The fibers with smaller initial modulus are more located in the outer layer, and the fibers with larger initial modulus are more located in the inner layer. Reasonable selection of fibers with different properties can be spun into different styles of yarns to adapt to different fabric uses or improve wear performance. Since chemical fibers can be arbitrarily selected in terms of length, fineness and fiber cross-sectional shape, the outerwear fabrics should be blended with cotton and chemical fibers with slightly thicker fibers and shorter lengths to increase the texture of the yarn surface.

Underwear fabrics carpet yarn should choose chemical fibers with slightly thinner fibers and longer lengths, so that cotton fibers are on the outer layer of the yarn to improve moisture absorption performance and wearing comfort. Open-end spinning includes yarns spun by air spinning, electrospinning, vortex spinning, etc. Due to the less inward transfer of fibers during twisting, the yarn core is tighter on the inside and loose on the outside than the outer layer, the structure is looser, and the fiber straightness Poor, the cohesion between fibers is poor, the yarn strength is low, but the dyeability and wear resistance are good. The yarn spun from self-twisting spinning is also called self-twisting yarn. It uses the twisting roller to produce periodic positive and reverse false twists on the whiskers. Periodic non-twist points appear on the finished yarn, so the strength is low. The strands are then woven.