Yarn Stiffness
The resistance of a yarn to bending forces determines the hand feel and drape of the final fabric. Yarn flexural rigidity measures the torque required to bend a yarn through a specific angle, representing its inherent stiffness. This property depends on both the material composition and the structural arrangement of the fibers within the yarn.
It is a fundamental measurement for predicting the tactile quality of knit and woven products. Stiffer yarns produce fabrics that are stiff and harsh to the touch, while flexible yarns yield soft, comfortable garments that drape naturally over the body.
Fiber Influence
Fiber diameter and cross-sectional shape are the primary drivers of this mechanical behavior. Coarse fibers with large diameters have much higher bending resistance than fine fibers. In addition, synthetic fibers with hollow cross-sections show different bending behaviors than solid fibers.
Spinning mills select specific fiber profiles to control the flexibility of the resulting yarn.
Fabric Softness
Twist level also affects the stiffness by locking the fibers together and limiting their movement. High-twist yarns like crepe are extremely stiff because the fibers are tightly bound and cannot slide past each other during bending. Conversely, low-twist yarns remain soft and flexible, though they are more prone to pilling and abrasion.
Balancing twist and flexibility is a key challenge in yarn design.
Spinning Variable
Knitting machines require yarns with low bending resistance to form clean, uniform loops without needle damage. Stiff yarns can cause tension spikes and yarn breakage during high-speed knitting. This operational constraint makes the measurement of yarn stiffness critical for knitting factories.
