Constant-length System And Constant-weight System
The constant-length system and constant-weight system are two yarn count systems that express yarn thickness through the relationship between length and weight, and they are notation methods in which the way the numbers indicate thickness is opposite.
Contents6 sections
Definition and Overview
The constant-length system expresses yarn thickness by the length per a fixed weight; with the same weight, the longer the length, the finer the yarn. Cotton count and metric count are examples, and the larger the number, the finer the yarn.
The constant-weight system expresses yarn thickness by the weight per a fixed length. Tex, decitex, and denier are typical examples, and with the same length, the heavier the yarn is, the thicker it is, so the larger the number, the thicker the yarn.
- Constant-length system: the larger the number, the finer the yarn
- Constant-weight system: the larger the number, the thicker the yarn
Relationship to Yarn Count
Yarn count is a general term for indicating yarn thickness, but the way the number is read is opposite depending on whether it is the constant-length system or the constant-weight system. For that reason, do not compare yarn thickness by the yarn count value alone; check the unit used, the material, and whether it is single yarn or plied yarn.
Denier and decitex are constant-weight systems and are often used for filament yarns. On the other hand, cotton count and similar systems are constant-length systems and are often used for spun yarns. However, material and yarn count systems do not always correspond one-to-one.
Effect on Hand Feel and Fabric Design
As yarn becomes finer, it is generally easier to bring out a delicate, smooth surface and a light feel. Thicker yarn tends to create thickness, presence, and a textured surface more easily. However, the hand feel of fabric also changes greatly depending on twist, weave or knit structure, density, and finishing.
The constant-length and constant-weight systems are methods for expressing yarn linear density, and they do not in themselves determine moisture absorption, warmth retention, stretch, or shrinkage. When planning, it is important to check not only the yarn count but also the blend ratio, fabric weight, density, and finishing processes.
Applications and How to Choose
Fine-count yarns are considered for lightweight shirts, blouses, linings, and lightweight knits. Thick-count yarns are used in designs that call for a solid look and durability, such as denim, canvas-style fabrics, and heavy jersey. Do not decide applications by yarn count alone; confirm the fabric appearance and strength with trial production.
In specifications and fabric standards sheets, make sure to state the unit for the yarn count notation. Since values from different systems cannot be compared directly, when handling overseas standards or supplier documents, check the distinction between the constant-length and constant-weight systems, the notation for single yarn or plied yarn, and the conversion conditions.
Notes on Washing and Sewing
Shrinkage and shape change after washing are affected not by the yarn count system but by the type of fiber, yarn twist, fabric structure, and finishing processes. For natural fibers or fabrics that have not been shrink-treated, perform pre-washing or a test wash before cutting, and reflect the shrinkage rate in the pattern and cutting allowance.
Thin fabrics made with fine yarn may make needle holes, puckering, and broken ground yarn more noticeable. Choose a sewing machine needle, sewing thread, and thread tension that suit the fabric, and do a test seam before sewing. For fabrics made with thick yarn, also check the thickness caused by overlapping seam allowances.
Frequently Asked Questions
In the constant-length and constant-weight systems, what happens to the yarn as the number gets larger?
In the constant-length system, the larger the number, the finer the yarn; in the constant-weight system, the larger the number, the thicker the yarn. If you judge thickness only by whether the number is large or small, you may read it the wrong way, so be sure to check units such as cotton count, decitex, and denier.
If the yarn count is the same, are the fabric thickness and hand feel also the same?
Not necessarily. Fabric thickness and hand feel are affected not only by yarn count but also by the material, twist, single yarn or plied yarn, weave or knit structure, density, fabric weight, and brushed or resin finishing. Judge by both the fabric sample and the specification values.
