Quality control in cotton yarn: which tests, which report

The most common mistake when buying yarn is reducing quality to a single number. Yarn is a combination of several independent properties, and the one that decides an application can be secondary in another. This article explains what each property means and which report a buyer can ask for.

The measured properties of yarn

Evenness describes the variation in cross section along the yarn and is usually given as a CV percentage. High irregularity shows up as streaks in woven fabric and as surface defects in knits. The thin place, thick place and nep counts reported alongside it show what kind of faults occur and how often.

Hairiness is the amount of fiber ends protruding from the yarn body. It affects handle and pilling tendency in knits, and sizing behavior in weaving. Strength and elongation at break determine whether the yarn will withstand the tension on a loom. To these are added twist measurement and conditioned moisture content.

Micronaire and staple length are not the same thing

These two are often used interchangeably, yet they measure different properties. Staple length is the length of the fiber, usually reported as upper half mean length in millimeters or inches. It is the precondition for spinning fine counts.

Micronaire reflects fineness and maturity together and has nothing to do with length. Low micronaire usually means immature fiber: dye uptake becomes uneven and neps increase. High micronaire means coarse fiber, fewer fibers in the yarn cross section and more irregularity. In short, length determines the count you can reach, while micronaire determines how that yarn will behave.

The report a buyer should ask for

A report by lot should contain at least the following: yarn count and twist, evenness value, thin place, thick place and nep counts, hairiness, strength and elongation at break. On the raw material side, staple length, micronaire and strength values can also be requested.

One thing matters as much as the report itself: which lot it belongs to. A report without a lot number cannot be matched to the goods received and therefore carries little practical meaning. Agreeing before the order on how a lot is defined, how often sampling occurs and what deviation is acceptable settles most later disputes in advance.