Spun yarn is made by twisting or otherwise bonding staple fibres together to make a cohesive thread, or "single."  Twisting fibres into yarn in the process called spinning can be dated back to the Upper Paleolithic,  and yarn spinning was one of the very first processes to be industrialized. Spun yarns may contain a single type of fibre, or be a blend of various types. Combining synthetic fibres (which can have high strength, lustre, and fire retardant qualities) with natural fibres (which have good water absorbency and skin comforting qualities) is very common. The most widely used blends are cotton-polyester and wool-acrylic fibre blends. Blends of different natural fibres are common too, especially with more expensive fibres such as alpaca, angora and cashmere. Bamboo yarn is a less expensive type that is a recent innovation.
Yarns are selected for different textiles based on the characteristics of the yarn fibres, such as warmth (wool), light weight (cotton or bamboo), durability (nylon is added to sock yarn, for example), or softness (cashmere, alpaca). Acrylic yarn is the least expensive.
Yarns are made up of a number of singles, which are known as plies when grouped together. These singles of yarn are twisted together (plied) in the opposite direction to make a thicker yarn. Depending on the direction of this final twist, the yarn will be known as s-twist or z-twist. For a single, the direction of the final twist is the same as its original twist.
Filament yarn consists of filament fibres (very long continuous fibres) either twisted together or only grouped together. Thicker monofilaments are typically used for industrial purposes rather than fabric production or decoration. Silk is a natural filament, and synthetic filament yarns are used to produce silk-like effects.
Texturized yarns are made by a process of air texturizing (sometimes referred to as taslanizing ), which combines multiple filament yarns into a yarn with some of the characteristics of spun yarns.