Singles and multiple-ply yarns
Yarns are made up of plies, which are the individual strands of yarn that are twisted in the opposite direction from how the single plies were spun.
The thinner the individual strands are, the softer garments it produces. This process makes the yarn stronger, so a ‘2-ply’ yarn generally offers higher quality than is seen in a ‘singles’ yarn (‘1-ply’ yarn), mainly because of the offset of the torque that exists in a ‘singles’ yarn.
Multiple plies are used by knitting mills to add colour or weight to the garment, but anything more than ‘2-ply’ yarn does not correspond necessarily with an increase of quality.
Even though some countries relate the number of plies with the thickness of the yarn, usually the number of plies does not affect how bulky the finished yarn will be.
You can have a bulky ‘two-ply’ yarn or a skinny ‘four-ply’ yarn, depending on how the individual ‘singles’ yarns were spun.
Fig.4 above illustrates how ‘ply’ yarns can also be plied among themselves, producing what is known as a ‘cabled’ yarn.
To make a ‘cabled’ yarn, ‘singles’ are spun with the twist in one direction, then plied in the opposite direction, and finally, the plies are plied together in the same direction that the ‘singles’ were spun.
As a result, very stable and sturdy yarn is produced, ideal for cable knit sweaters.