S Twist And Z Twist

Definition and Overview

Twist is the process of twisting a bundle of fibers or a single yarn in a spiral to give it cohesion, strength, and surface texture. When a yarn is held vertically, the twist whose slope appears in the same direction as the central line of the letter S is called S twist, and the twist whose slope appears in the same direction as the central line of the letter Z is called Z twist.

The twist direction is a specification separate from the yarn’s thickness and material name. Because properties also change depending on the raw material, number of twists, and whether it 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 or 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 have the twist direction of the single yarns and the direction used to ply them opposite to each other. Such a structure suppresses the tendency of twist to return and affects yarn handling and shape stability.

• Single yarn: one yarn made by twisting fibers together.
• Ply yarn / multi-twist yarn: a yarn made by combining multiple single yarns and twisting them further.
• Number of twists: the number of twists applied per unit 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 in some systems of the same count notation, a larger number indicates a finer yarn. 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 the count or nominal count. For example, even with the same count, if the material, number of twists, twist direction, or structure of single yarns and ply yarns differs, the appearance, firmness, and behavior during sewing may not be the same.

Main Applications

Twist direction may be managed for woven and knitted yarns, as well as sewing machine thread, hand-sewing thread, and embroidery thread. In particular, in sewing and decoration that use multiple yarns, it can affect yarn twist, light reflection, and the appearance of seams.

In textiles, yarns with different twist directions may be combined in warp and weft, or differences in twist direction and number of twists may be used. However, the final appearance and physical properties of the textile are also determined by the weave or knit structure, density, dyeing and finishing, and other factors.

How to Choose and Sewing Precautions

When specifying or selecting yarn, check not only whether it is S or Z, but also the material, count or denier, yarn structure, twist strength, and application. In repairs to existing items or additional production, even if the yarn looks the same thickness, differences in twist structure can affect the appearance of the seam and textile surface.

When sewing with a machine, yarn twisting, seam shrinkage, and puckering may occur depending on the machine’s looper and needle, sewing conditions, and the combination with the textile. Before mass production, it is important to sew test samples using the actual textile and accessories, and confirm the seam appearance and strength.

S twist and Z twist indicate the direction of twist, whereas strong-twist yarn refers to yarn with a high number of twists. Also, single yarn and ply yarn are categories based on the number of strands and structure that make up the yarn. These are related to each other, but they do not mean the same thing.

Frequently Asked Questions

Which is right twist, S twist or Z twist?

There is variation in how the terms are explained depending on how the yarn is viewed and common industry usage, so it is safest to avoid specifying only right twist or left twist. When the yarn is placed vertically, indicate the slope of the spiral with S or Z, and if necessary, confirm with a physical sample or specification sheet.

Should I choose S twist or Z twist for sewing machine thread?

The twist direction of sewing machine thread relates 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 being used, then perform a test seam to check for twisting and seam irregularities.

If S twist and Z twist differ, does the yarn thickness also change?

The twist direction itself is not an item that indicates thickness. Yarn thickness is checked by count or denier. However, even with the same indicated thickness, if the number of twists, yarn structure, or material differs, the bulkiness and tightness can change, and the apparent thickness and hand may differ.