In the previous article, we learned to tell different fabric materials apart using fiber length. But length alone isn’t enough to fully identify cloth ingredients. Today, we’ll dive deeper into the “internal properties” of fibers. We’ll explore linear density and mechanical properties to unlock more practical tips for distinguishing fabric materials.
Linear Density: Labeling Fibers by “Thickness”
If length is the “external shape” of a fiber, linear density is the key indicator describing its “thickness”. Simply put, linear density refers to the mass of fibers or yarns per unit length. It directly shows how thick or thin a yarn is—the higher the linear density, the thicker the fiber or yarn. This indicator not only affects the fabric’s feel and breathability but also helps distinguish different raw materials.
Linear density is one of the core physical and geometric characteristics of fibers. Its official international unit is tex (T). It’s defined as “the mass in grams of a 1-kilometer-long fiber or yarn”. For example, if a 1-kilometer-long yarn weighs 20 grams, its linear density is 20tex.
However, in actual production and trade, there are other common linear density units besides tex. These include the British English count (S), which represents the number of 840-yard lengths in 1 pound of yarn (higher count means thinner yarn); the metric metric count (N), referring to the number of kilometers in 1 kilogram of yarn (higher count means thinner yarn); and denier (D), often used for chemical fibers and filaments. Denier is the mass in grams of 9000 meters of fiber (higher number means thicker fiber).
Different fiber materials usually have typical linear density ranges. Natural cotton fibers, for instance, usually have a linear density between 1.5–2.5tex. Ramie fibers, being thicker, have a linear density of 3–6tex. Chemical fibers like polyester filaments can have their linear density adjusted as needed, ranging from a few tex to dozens of tex. By measuring linear density and comparing it with typical ranges, we can quickly narrow down the possible raw materials.
Mechanical Properties: The Secret of Fiber “Toughness and Elasticity”
If linear density describes the “static thickness” of fibers, mechanical properties show how fibers behave when 受力. They tell us how strong and elastic fibers are. Different materials have distinct mechanical properties, which helps us tell them apart.
① Breaking Length: A Clear Measure of Fiber “Load Capacity”
Breaking length is a useful indicator. It refers to the equivalent length of a single fiber when the hanging gravity equals its breaking strength. Simply put, when a fiber is hung and weight is added below until it breaks, the total length of the hanging fiber is its breaking length. This indicator turns the fiber’s breaking strength into an easier-to-understand length value. It directly reflects the fiber’s maximum load capacity under gravity—the longer the breaking length, the stronger the load capacity.
For example, cotton fibers usually have a breaking length of 20–30 kilometers. Polyester fibers can reach 35–50 kilometers. That’s why polyester fabrics are more wear-resistant and tear-resistant.
② Modulus: Measuring Fiber “Resistance to Deformation”
Modulus, more precisely elastic modulus, shows how well a fiber resists deformation. When we stretch a fiber, high-modulus fibers are “stiffer” and hard to stretch. Low-modulus fibers are “softer” and deform easily under light force.
Among natural fibers, hemp fibers have high modulus. So ramie and flax fabrics are usually crisp, stylish, and wrinkle-resistant. Wool has low modulus, making wool fabrics soft and fluffy to the touch. Chemical fibers like polyester have high modulus, making their fabrics crisp and durable. Spandex has very low modulus but super elastic recovery. It’s often used in stretchy sportswear fabrics.
③ Breaking Elongation: Direct Proof of Fiber “Elasticity”
Breaking elongation is the key indicator of fiber elasticity—the higher the breaking elongation, the better the fiber’s elasticity. It’s defined as the ratio of the fiber’s elongation at break to its original length, usually expressed as a percentage. For example, a fiber 10 cm long that stretches to 15 cm before breaking has a breaking elongation of 50%.
Different fibers have very different breaking elongations. Cotton fibers have low breaking elongation, usually 3%–7%. So cotton fabrics have poor elasticity, wrinkle easily after stretching, and don’t recover well. Spandex has a breaking elongation of 400%–700%, which is why it can stretch a lot and bounce back quickly. Polyester has a breaking elongation of 20%–50%, with both elasticity and stability. That’s why it’s often blended with cotton to improve fabric elasticity and wrinkle resistance.
By understanding fiber thickness through linear density and judging load capacity, deformation resistance, and elasticity through mechanical properties, we have a more comprehensive basis for distinguishing fabric materials. In the next article, we’ll discuss fiber hygroscopicity and other properties to help you fully master the “skills” of distinguishing fabric raw materials.
