Doubling is a textile industry term synonymous with combining. After spinning, yarn is doubled for many reasons. Yarn may be doubled to produce warp for weaving, crochet and knitting. It is used for embroidery threads and sewing threads.
Doubling of yarn where two or more stands or ends of yarn are twisted together. There are many purposes where doubled yarn is used. Sometimes thread is doubled to make warp, and it is invariably used for the manufacture of knitting yarn, crochet yarn and sewing yarn. All these yarns must be smooth and free from knots.
In a sewing thread, the treads are doubled in two phases. Two or three strands are twisted together then three of these threads are twisted together, to form a six or nine ply. The spun yarn is wound onto a bobbin using a doubling winding machine, and two or more of these bobbins are placed on doubling frame (doubling winding machine). The ends pass through a series of rollers and twisted together onto one bobbin using a spindle and flyer.