Yarn Evenness and Imperfections
topic
Yarn evenness is quantified by CVm% (coefficient of variation of mass per unit length) measured by the Uster Tester at 400 m/min test speed. World-class CVm% for ring-spun cotton 30 Ne: 10–12%. Imperfections are counted per 1000 m: thin places (−50% threshold), thick places (+50%), and neps (+200%). Uster Statistics benchmark these values against global production. CVm% and IPI (thin + thick + neps total) are the primary yarn quality specifications in trade.
Role
Yarn evenness is the foundational quality specification for all downstream processes. High CVm% causes fabric barre, uneven dyeing, and variable fabric weight — defects that are impossible to correct after weaving or knitting. CVm% is the first test performed on every yarn lot in quality control, and its deviation from specification is the most common reason for yarn rejection at the mill gate.