knop

A knop is a localized thickening in yarn caused by a tuft of looped or twisted fibers bunching together. It appears as a small, rough lump on the yarn surface, typically 3 to 8 millimeters long, and creates visual and tactile irregularity in the finished fabric. Knops are common in spun yarns, particularly those made from staple fibers like cotton, wool, and polyester blends, where short fiber lengths are twisted together.

The defect forms during yarn production when fibers fail to integrate smoothly into the main yarn body. In roving and spinning, if tension drops momentarily or if fibers bunch at the drafting zone, they wrap around the yarn axis rather than aligning parallel to it. The result is a knot-like accumulation that cannot be combed out once the yarn is spun and set. Knops are distinct from neps (small fiber knots) because knops involve actual loop formation, not just fiber entanglement.

Impact on Production and Fabric

Knops cause visible defects in woven and knitted fabric, appearing as small bumps or thickened spots that break pattern uniformity. In fine fabrics, particularly those for apparel, even one knop per thousand meters of yarn becomes objectionable. They also create weak points: the looped structure within a knop does not contribute to yarn strength, and the irregular geometry can catch during processing, leading to snarling or breakage on looms or knitting machines.

Quality control in yarn mills involves periodic visual or automated inspection. High-speed electronic yarn cleaners can detect and remove some knops by monitoring yarn diameter and can either break the yarn for manual removal or, on some systems, attempt mechanical smoothing. However, detection is imperfect, especially in colored or textured yarns where visual inspection becomes difficult. Spinners reduce knop formation by maintaining consistent roving preparation, controlling drafting tension, and using well-carded or combed fiber stocks.

The term derives from the Old English cnop, meaning a knot or lump, and appears in textile vocabulary across Germanic languages. It remains standard terminology in spinning mills and yarn testing laboratories, where knop count per unit length is a defined quality metric, though the threshold for acceptability varies by yarn type, end use, and market region.