S Twist And Z Twist
S twist and Z twist are terms that describe the direction of twist applied to the fibers or single yarns that make up yarn, by comparing it to the diagonal strokes of the letters S and Z.
Contents6 sections
Definition and Overview
Twist refers to the process of spirally twisting a bundle of fibers or a single yarn to give it cohesion, strength, and surface texture. When a yarn is held vertically, the one whose spiral slope looks the same direction as the center stroke of S is called S twist, and the one whose spiral slope looks the same direction as the center stroke of Z is called Z twist.
Twist direction is a specification separate from yarn thickness or material name. Because properties also vary depending on the raw material, the number of twists, and whether the yarn is a single yarn or a yarn made by combining multiple yarns, the strength or hand of a yarn cannot be judged from the S/Z notation alone.
Materials, Twist, and Structure
S twist and Z twist are ways of indicating twist direction used for spun yarns and filament yarns made from various fibers such as cotton, wool, linen, silk, and synthetic fibers. This is not a classification of the material itself, but information about the structure used when making the yarn.
When combining multiple single yarns, it is common to make the twist direction of the single yarns and the direction used to ply them opposite to each other. Such a structure suppresses the force that tries to untwist the yarn and affects ease of handling and shape stability.
- Single yarn: one yarn made by twisting fibers.
- Ply yarn / multiple-ply yarn: a yarn made by combining multiple single yarns and twisting them further.
- Twist count: the number of twists applied per a given length, managed separately from twist direction.
Relation to Thickness Notation
Yarn thickness is generally checked using notations such as count, denier, and tex. Count is mainly used for spun yarns, and within the same count system, larger numbers may indicate finer yarns. Denier, on the other hand, expresses thickness by mass per length.
S twist and Z twist are not units of thickness, so they are checked together with count or nominal count. For example, even with the same count, appearance, firmness, and behavior during sewing are not necessarily the same if the material, number of twists, twist direction, or single-yarn / ply structure differs.
Main Applications
Twist direction may be managed for woven yarns, knitting yarns, as well as sewing machine thread, hand-sewing thread, and embroidery thread. In particular, in sewing and decoration using multiple strands, it can affect yarn twisting, light reflection, and the appearance of the stitches.
In textiles, threads with different twist directions may be combined for warp and weft, or differences in twist direction and twist count may be used. However, the final appearance and physical properties of the textile are determined together with the weave structure, density, dyeing and finishing, and other factors.
Selection and Sewing Considerations
When specifying or selecting thread, check not only whether it is S or Z, but also the material, count or denier, thread structure, twist strength, and application. When repairing existing products or making additional production, even if the thread looks the same thickness, differences in twist structure can create differences in the appearance of the seam and textile surface.
When sewing with a machine, thread twisting, seam shrinkage, and puckering may occur depending on the machine’s loopers or needles, sewing conditions, and the combination with the textile. Before mass production, it is important to test sew with the actual textile and accessories and confirm the appearance and strength of the seam.
S twist and Z twist indicate twist direction, whereas a hard-twist yarn refers to a yarn with a large number of twists. Single yarn and ply yarn are categories based on the number of strands and structure that make up the yarn. These are related to one another, but they do not mean the same thing.
Frequently Asked Questions
Which is right twist, S twist or Z twist?
Because the naming can vary depending on how the yarn is viewed and on industry convention, it is safest to avoid specifying only right twist or left twist. Indicate the spiral slope as S or Z when the yarn is placed vertically, and confirm with an actual sample or specification sheet if necessary.
For sewing machine thread, should I choose S twist or Z twist?
The twist direction of sewing machine thread is related to compatibility with the machine mechanism and sewing method, but it cannot be chosen uniformly based on application alone. Check the thread maker’s specifications according to the machine, needle, sewing specifications, and textile to be used, then perform a test sew and confirm twisting and irregular stitches.
If S twist and Z twist differ, does the yarn thickness also change?
Twist direction itself is not an item that indicates thickness. Yarn thickness is checked by count or denier. However, even when the indicated thickness is the same, if the twist count, yarn structure, or material differs, bulkiness and firmness may change, and the apparent thickness and hand may differ.
