Yarn is divided into: (1) staple fiber yarn, which is made of staple fiber (natural staple fiber or chemical fiber cut fiber) through spinning, divided into ring yarn, free end spinning, self-spinning yarn, etc. (2) Continuous filaments, such as natural silk and chemical fiber filaments, with or without filament, smooth filaments or deformed filaments, etc. (3) Combination yarn of staple fiber and continuous filament, such as polyester-cotton filament core-spun yarn, etc. The thread is made up of two or more strands of single yarn combined and combined.

The fineness of the yarn can be expressed in various ways, such as number, metric count, imperial count, denier, etc. (see count). The twist of the yarn is expressed in terms of the number of twists per meter or inch. The direction of twisting back is divided into S twist and Z twist. Within a certain range of twist, the strength of the yarn increases with the increase of twist. The twist direction of the single yarn and the twist direction of the strand are selected according to the use of the strand. Usually the single yarn is twisted in the opposite direction to the strands, i.e. ZS or SZ. There is an optimal ratio of the tension between the single yarn and the strand, in this range, the strand strength increases with the increase of the strand tension, and the strand strength decreases when the critical value is exceeded. The properties of the fibers and the spinning method play a decisive role in the properties of the yarn. In the twisting process of ring 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 fibers are spiral around the axis of the yarn, and the spiral radius increases or decreases alternately along the axial direction. At this time, the longer fibers tend to the axis of the yarn more, and the shorter fibers tend to the outer layer of the yarn. The fineness of the fiber tends to the axis of the yarn, and the fineness of the fiber tends to the outer layer of the yarn. Fibers with a smaller initial modulus are more likely to be located in the outer layer, and fibers with a larger initial modulus are more likely to be located in the inner layer. Reasonable selection of fibers with different characteristics can be spun into different styles of yarn, suitable for different fabric uses or improve wearing performance. Since the length, fineness and cross-sectional shape of the fiber can be arbitrarily selected for the outerwear fabric, the outer fabric should be blended with chemical fiber and cotton with slightly thicker fiber and shorter length to increase the wool feeling on the surface of the yarn. It is advisable to use chemical fibers with slightly thinner fibers and longer lengths for underwear fabrics, so that the cotton fibers are in the outer layer of the yarn to improve moisture absorption and wearing comfort. Free end spinning includes air-spinning, electro-spinning, vortex spinning and other spun yarns, because the fiber is less transferred inward during twisting, the yarn core is tighter inside and loose than the outer layer, the structure is looser, the fiber straightness is poor, the holding force between the fibers is poor, the yarn strength is low, but the dyeability and wear resistance are good. The yarn spun from self-twisting spinning, also known as self-twisting yarn, is the use of rolling rollers to produce periodic forward and reverse false tension on the whiskers, and there is a periodic no point on the yarn, so the strength is low, and it is generally woven after strands are formed.

Filament yarn is a bundle of filaments (such as natural silk, chemical fiber silk or rayon) that are combined together; There are mainly polyester filament, viscose filament, nylon filament, etc.