Yarns are threads produced by drawing and twisting together of fibres. They are the basic material used for making various apparels and fabrics. Yarns are made up of any number of plies, each ply being a single spun yarn. These single ply of yarn are twisted in the opposite direction together to make a thicker yarn. Depending on the direction of this final twist, the yarn will be known as s-twist or z-twist.
The two main types of yarn are filament yarns and spun yarn. Filament yarn is made when two or more filaments or yarns are drawn and twisted together which stretches the yarns slightly.
Spun yarn is made from staple fibres also known as shorter fibres. These include all natural fibres except silk, but may also include synthetic filaments which have been cut to form staple fibres.
Staple fibres are made into a yarn by combing to straighten the fibres, drawing, and spinning. Staple yarns tend to be bulkier, softer, and less lustrous than filament yarns, which are usually used for smooth, shiny fabrics. However, filament yarns can be given different textures, by different texturing and bulking processes.
Filament yarn is smooth, so the fabric make of filament yarn has larger tenacity than the fabric made of staple yarn, as well as greater air permeability. Filter fabric made of staple yarn has hair on the surface, so it is better than filter fabric made of filament yarn for dust collection and pressure filtration. While the fabric made of filament yarn has smooth surface and high air permeability, so it is suitable for liquid filtration. Silk is the only natural single filament yarn available in the market today.