CSP stands for count strength product, and it is the lea strength of a yarn in pounds multiplied by its English cotton count. It is the traditional way Indian spinners express yarn strength, and it lets you compare strength across counts because a finer yarn naturally breaks at a lower load but has a higher count number. A combed ring-spun cotton yarn usually has a CSP well above a carded yarn of the same count, and open-end yarn sits lower still.
Lea strength is measured by winding 120 yards of yarn into a skein, called a lea, and breaking the whole skein on a lea tester. The result in pounds is multiplied by the count in Ne to give CSP. Because the test breaks many strands at once, it averages out weak places and gives a stable figure, but it also hides how variable the yarn is from place to place.
Single-thread strength and tenacity
Modern spinning mills increasingly report single-yarn strength instead of lea strength, measured on a tensile tester that breaks one strand at a time at a set speed. The result is given as tenacity, usually in centinewtons per tex or grams per tex, together with elongation at break. This is the figure Uster statistics benchmark, and it is more relevant to how yarn behaves on a high-speed loom or knitting machine, where a single weak place causes a stop.
The two measurements are not directly convertible, and a yarn with a good CSP can still have poor single-thread results if it has occasional weak spots. Ask for both when you can. If the mill reports only CSP, request the coefficient of variation of lea strength as well, since a high CV means the average is hiding weak leas.
What a buyer should specify
- The count and the tolerance on count, since a yarn spun slightly coarse will show a better lea strength than the contract count deserves.
- Minimum CSP or minimum tenacity, with the test method named, for example ASTM or ISO single-yarn tensile testing.
- Elongation at break, because low elongation yarn breaks more on knitting machines even when tenacity is adequate.
- The conditioning requirement, as cotton yarn tested dry reads differently from yarn conditioned at standard humidity.
- Whether results are from the actual lot or from a general mill specification sheet.
Reading a test report
Look first at the count actually spun, then at strength, then at the variation figures. A report showing an unusually high CSP alongside a count slightly coarser than contract is a sign that the mill is meeting strength by adding mass, which costs you in fabric weight and yarn consumption. Compare the strength figures with the mill's own earlier lots rather than only against the contract minimum, so you can see whether quality is drifting.
How Creston & Co helps
We draw sealed samples from the lot at the mill and send them to an NABL-accredited lab so that strength and count are verified independently, not only on the mill's own report. We visit the spinner before the first order, audit the testing laboratory, and send weekly updates while the order runs. If you want help setting a workable CSP or tenacity specification, we offer a free 20-minute sourcing review.