WARP AND WEFT. Warp threads are those which run lengthwise of the fabric; weft threads run transversely. In the actual manufacturing of practically all kinds of woven tex tures, there is a considerable difference between the two : ( The raw material from which warp is made is almost invariably of a higher grade than that used for weft. ( 2 ) The number of turns per inch or the "twist" in warp threads usually exceeds the twist in the weft threads or picks. (3) Multiple-fold or multiple ply yarns (two or more single threads twisted together) are more often used for warp than for weft. (4) Coloured threads appear in both, but much more frequently in the warp than in the weft.
(5) The fibrous material from which warp threads are made may be the same as that used for the weft threads, or the two may be of entirely different kinds. (6) Warp threads are often starched or sized, but weft threads are seldom treated in this way.
With the exception of knitted fabrics or other similar struc tures in which one series of yarns only is used, the warp and weft threads interweave together, not only to form the struc ture of the fabric but also to adorn it with more or less complex designs. (See WEAVING.)