Single Yarn – fiber which is spun in one direction, usually S twist to create a basic yarn.
2-Ply Yarn – 2 singles which have been spun in the same direction and then plied in the opposite direction.
3-Ply Yarn – A yarn that consists 3 singles which have been spun in the same direction and then plied in the opposite direction.
Crepe Yarn – A yarn that consists of a 2-ply yarn plied with a single yarn spun with the same twist as the ply (Z)
Cable Yarn – A yarn that consists of two 2-ply yarns which are plied together in the opposite direction of the last ply.
Coil Yarn – A 2-ply yarn in which a single is allowed to wrap around a core yarn by holding the single at a right angle to the yarn. A third ply in the opposite direction can be used to anchor the yarn.
Twist is stored (potential) energy. We mechanically add energy to the yarn when we use force to act on the spindle. The action of twisting the spindle, transfers that energy into the yarn. This is why, if you let go of a single after spinning it, it untwists itself. It is releasing the stored energy. This is also why knitting with singles produces skewed stitches. The energy has to go somewhere.
For a balanced yarn, we need a second ply. Each of the two singles stores energy. When those singles are twisted together in the opposite direction, the twist energy is released… into the other single. Essentially you have two singles pushing energy toward each other. The energy is still stored, but is now being carried between the two plies.
The Math of Multi-Ply Yarns
If you are spinning multi-ply yarns, you will need to use extra twist in each ply except for the last ply, which gets the normal amount of twist.
If you take two 2-ply yarns that have been plied to the normal amount and ply those together to make a cabled yarn, the cable ply reverses the ply you put into the 2-plies.
(1.5S+1.5S)/1Z = Balance