Twist in yarn is not only necessary to hold the yarn together, it is as important as the fiber in determining the quality of the finished yarn. When we learn to spin, it is drilled into our heads that we must spin our singles clockwise (Z twist) and ply our yarn counterclockwise (S twist). How does twist affect our finished yarn?
Many times we focus on the quality of the spinning fiber and preparation because we know that it will affect the quality of the yarn. Too often, we overlook the fact that we are spinners, we can make a silk purse from a sow’s ear. Using the correct amount of twist and balancing the finished yarn, can make even a mediocre fleece into a lovely yarn.
Why do we spin and ply in different directions? To balance the energy in the yarn. As we spin our singles, we are adding energy to the fiber that will hold the fibers together. Imagine using a single prop to hold up a tree. All of the support is on one side, so when the wind blows from the other direction, the tree is still going to fall down. A single ply yarn works the same way. It will not respond well to abrasions of normal wear, and if it is too twisted it will tend to double back on itself. But if you take two or more singles that are spun in one direction, and ply them in the opposite direction, the yarn becomes not only stronger, but it will also become softer. The fibers and twist energy form a network to hold the tree upright.
The amount of twist is determined by the nature of the fiber. The longer the staple length, the less twist required to make a structurally sound yarn. Also, the more crimp a fiber has, the less twist it will need to create a successful yarn.
The desired yarn result also dictates the amount of twist to impart upon the fiber. For example: to create a boucle yarn, one ply is intentionally overspun and allowed to loosely feed off of the bobbin during the plying process creating tendrils in the yarn. Another option is to create a bubble yarn by plying a single or, even a decorative sewing thread, around a pencil roving.
The rule of spinning to the Z (clockwise) direction and plying to the S (counterclockwise) is not a law of nature. You can reverse them and still create a perfectly balanced yarn (and lightning will not strike you down). It is just a starting point, as are all of the “rules” of spinning.