Thread Twist Explained
- S Twist
- Z Twist
What is S Twist and Z Twist?
Recently, there has been a lot of talk about S twist and Z twist threads and it's getting attention. Some refer to thread twist as a left or right twist, but the proper terminology is S or Z twist. When a sewing thread is constructed, it is made up of multiple strands, usually two or three strands (also referred to as plies or ply) twisted together, although some may have as many as six or eight strands twisted together. All sewing, embroidery, or quilting threads made for home machines, industrial machines, or longarm machines should have a final Z twist pattern.
The initial twist (or first twist) for the individual strands should be an S twist. These strands are then twisted together in a final Z twist to form the thread. This is the same worldwide for any major brand of sewing, embroidery, or quilting machine. There are a few threads that have the opposite twist. Some hand quilting thread, knitting, and weaving threads have a final S twist. If you use a thread with an opposite twist, the thread will loosen instead of tighten as you sew with it. Threads are not marked with the twist pattern because it isn't considered essential to know. If you use quality thread from a reliable company and stitch with it in its intended purpose, most likely it has the proper twist. If you notice that your thread unravels as it sews, it is probably a thread not intended for machine work.
S twist and Z twist visualized
Z twist threads are designed for machine sewing
Although it is never printed on labels, thread twist is measured by the number of twists applied per meter (approx. 3 feet). A loosely twisted thread requires less total fiber content, takes less time to produce, and is less expensive. It may have as few as 150 twists per meter. (Think of a budget serger thread that can easily be untwisted by rubbing it between your fingers.) A quality thread will have as many as 1,200 twists per meter, resulting in a smooth, consistent surface. A higher twist also condenses more thread into the space resulting in greater strength.
Here's an exaggerated example of how proper twisting affects the quality of thread: Take a large bath towel, lay it on the floor, and measure the length. Let's say it is 48 inches long. Roll the towel length-wise so you now have a rolled towel that is still 48 inches long. Start twisting the towel. Every 3-4 twists, re-measure the length and you will notice that you lose about two inches. Continue to twist the towel another 10 turns and the towel will be only about 36 inches long. We lost 25% of the length of the towel. The result, however, is a very smoothly rolled towel. The tightly twisted towel is also much stronger than a loosely twisted towel. The more twists applied, the smoother the surface becomes.
If we start with 10,000 yds. of untwisted thread and apply a loose twist, we will end up with 9,500 yds. of thread that is not high quality. If we apply the proper twist, the final measurement will be about 7,500 yds. A quality thread requires about 20% more fiber than a low quality thread. Like most things, you get what you pay for.