Yarn is a long continuous length of interlocked fibres, suitable for use in the production of textiles, sewing, crocheting, knitting, weaving, embroidery, or ropemaking. Thread is a type of yarn intended for sewing by hand or machine. Modern manufactured sewing threads may be finished with wax or other lubricants to withstand the stresses involved in sewing. Embroidery threads are yarns specifically designed for needlework. Yarn can be made from a number of natural or synthetic fibers, or a blend of natural and synthetic fibers. Spun yarn is made by twisting 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 first processes to be industrialized. Spun yarns are produced by placing a series of individual fibres or filaments together to form a continuous assembly of overlapping fibres, usually bound together by twist. 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. Knitting yarn is composed of twisted strands of fiber, which are known as plies when grouped together. These strands 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 have either s-twist (the threads appear to go "up" to the left) or z-twist (to the right). For a single ply yarn, the direction of the final twist is the same as its original twist. The twist direction of yarn can affect the final properties of the fabric, and combined use of the two twist directions can nullify skewing in knitted fabric.
Fiber or fibre is a natural or man-made substance that is significantly longer than it is wide. Fibers are often used in the manufacture of other materials. The strongest engineering materials often incorporate fibers, for example carbon fiber and ultra-high-molecular-weight polyethylene. Natural fibers or natural fibres are fibers that are produced by geological processes, or from the bodies of plants or animals. They can be used as a component of composite materials, where the orientation of fibers impacts the properties. Natural fibers can also be matted into sheets to make paper or felt. Natural fibers are good sweat absorbents and can be found in a variety of textures. Cotton fibers made from the cotton plant, for example, produce fabrics that are light in weight, soft in texture, and which can be made in various sizes and colors. Clothes made of natural fibers such as cotton are often preferred over clothing made of synthetic fibers by people living in hot and humid climates. Synthetic fibers or synthetic fibres are fibers made by humans through chemical synthesis, as opposed to natural fibers that are directly derived from living organisms, such as plants (like cotton) or fur from animals. They are the result of extensive research by scientists to replicate naturally occurring animal and plant fibers. In general, synthetic fibers are created by extruding fiber-forming materials through spinnerets, forming a fiber. These are called synthetic or artificial fibers. Man-made or chemical fibers are fibers whose chemical composition, structure, and properties are significantly modified during the manufacturing process. In fashion, a fiber is a long and thin strand or thread of material that can be knit or woven into a fabric. Man-made fibers consist of regenerated fibers and synthetic fibers.
A sweater (North American English) or pullover, also called a jumper, is a piece of clothing, typically with long sleeves, made of knitted or crocheted material, that covers the upper part of the body. When sleeveless, the garment is often called a slipover or sweater vest. Sweaters are worn by adults and children, often over a shirt, blouse, T-shirt, or another top, but sometimes next to the skin. Sweaters were traditionally made from wool but can now be made of cotton, synthetic fibers, or any combination of these. There are also seasonal sweaters, which around Christmas are called "ugly sweaters". The term "sweater" is a catch-all for a variety of knit garments. Although the term often refers to a pullover, it can also refer to a cardigan, a garment that opens and fastens down the front. Within either group, there is a great variety of designs. Various necklines are found, although the V-neck, turtleneck, and crew neck are the most popular. The hemline is typically at hip height or slightly longer, just overlapping the waist of one's pants or skirt, but can vary significantly. It can range from just below the bust in women's garments to mid-thigh in either sex or even longer in a knitted variation of the poncho shirtdress. The sleeve length is also variable, ranging from full-length or three-quarters to short-sleeved, cap sleeves or sleeveless. The front seam or opening of a cardigan allows for further different styles, such as a surplice or a bolero jacket. All hems may have various types of borders, such as picots, ribbing, and frills. Knitted fabrics are generally somewhat elastic and have a softer hand (feel or drape) than woven fabric. Sweaters that are more tightly fitted or have a soft drape may conform well to the body without requiring tailoring necessary in a woven garment such as darts, flares, and gores. Even when such shaping is used, it can be knit into the fabric itself, without requiring seams.