Neps are small knots of tangled fibers which are created during harvesting, ginning, and yarn manufacturing phases of production. They occur in varying numbers in most cotton yarns and cause considerable concern to most persons interested in yarn and fabric quality. Neps may be a source of trouble in manufacturing, detract from the appearance of the woven fabric, and may not dye properly. Seedcoat fragments, along with neps, affect not only the quality of the finished product but are probably responsible for some of the "ends down" in spinning.

There is some evidence that the number of neps in yarn increase with increase in fiber length, decrease in fiber weight per inch, and increases in percentage of thin-walled fibers. The literature indicate that ginned lint from machine-picked defoliated cottons may have more neps than the lint from undefoliated cottons, and fibers from late-harvested cotton are more susceptible to nepping than early-harvested cotton. This has been attributed to the likelihood of the defoliated and late-harvested cottons being more immature.