"In the textile arts, plying is a process used to create a strong, balanced yarn. It is done by taking two or more strands of yarn that each have a twist to them and putting them together. The strands are twisted together, in the direction opposite that in which they were spun. When just the right amount of twist is added, this creates a balanced yarn, one which has no tendency to twist upon itself. Almost all store-bought yarns are balanced, plied yarns. The word ply derives from the French verb plier, "to fold", from the Latin verb plico, from the ancient Greek verb πλέκω.
A two-ply is thus a yarn plied from two strands, a six-ply is one from six strands, and so on. Most commercial yarns are more than a two ply. Embroidery floss is generally a six-ply yarn, for example." - (en.wikipedia.org 16.04.2021)
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