The warp is the set of
yarns or other things stretched in place on a
loom before the weft is introduced during the weaving process. It is regarded as the
longitudinal set in a finished fabric with two or more sets of elements. The term is also used for a set of yarns established before the interworking of weft yarns by some other method, such as finger manipulation, yielding wrapped or twined structures. Very simple looms use a
spiral warp, in which the warp is made up of a single, very long yarn wound in a
spiral pattern around a pair of sticks or beams. The warp must be strong to be held under high tension during the weaving process, unlike the weft which carries almost no tension. This requires the yarn used for warp ends, or individual warp threads, to be made of
spun and
plied fibre. Traditionally natural fibres such as
wool,
linen,
alpaca, and
silk were used. However,
improvements in spinning technology during the
Industrial Revolution created
cotton yarn of sufficient strength to be used in mechanized weaving. Later,
synthetic fibres such as
nylon or
rayon were employed. While most weaving is weft-faced, warp-faced textiles are created using densely arranged warp threads. In these the design is in the warp, requiring all colors to be decided upon and placed during the first part of the weaving process, which cannot be changed. Such limitations of color placement create weavings defined by length-wise stripes and vertical designs. Many South American cultures, including the ancient Incas and Aymaras, employed
backstrap weaving, which uses the weight of the weaver's body to control the tension of the loom. ==Weft==