What Is Cotton, Really? Staple Length, Sea Island, Giza and Supima

Cotton grows as a seed hair. Each fiber is a single, greatly elongated cell that grows from the outer coat of the cottonseed, unlike a bast fiber such as linen, which comes from the plant’s stem, and it is mostly cellulose, typically 88.0 to 96.5 percent. The single biggest driver of quality is staple length, the average length of the fibers in a sample, because longer fibers spin into finer, smoother, stronger yarn with fewer loose ends poking out. Sea Island, Egyptian Giza, American Pima and Supima are the famous names built on that one property, and they are close cousins of each other, variations on a small handful of the same species.

One genus, two very different cottons

Almost all cotton grown for clothing belongs to the genus Gossypium. Gossypium hirsutum, called upland or Mexican cotton, supplies around 90 percent of world cotton production, though the exact modern split between species varies by source and by year, so that figure is best read as an order of magnitude. Gossypium barbadense is the other major species, grown specifically for longer, finer fiber, and it is the shared ancestor behind Sea Island, Egyptian and American Pima cotton. These are variations within the same long-staple lineage, distinguished mainly by where and how they are grown.

The famous long-staple names

Sea Island cotton has been grown in Barbados since at least the 1650s. The West Indian Sea Island Cotton Association (WISICA) is the body that inspects and certifies the crop today, and certified output is often cited at only around 130 bales a year, roughly 70 of them from Barbados, with the entire Barbados crop going to a single Italian mill. That specific figure is worth checking directly against WISICA before treating it as exact, though the scale it describes, a few dozen tons a year worldwide, is consistent with how the fiber is talked about across the trade.

Egyptian cotton growing began in 1819 or 1820, when the French engineer Louis Alexis Jumel introduced a Gossypium barbadense variety to Muhammad Ali Pasha, and Sea Island seed was imported into Egypt in 1827, feeding the same long-staple bloodline. Modern Egyptian cotton is graded by variety number: Giza 45, Giza 87, Giza 88, Giza 92, Giza 96 and others. The true extra-long-staple grades are a small share of Egypt’s total crop. Giza 45 alone is often put at about half of one percent of the annual harvest, an industry estimate and not an audited figure, and it is hand-picked in three or four passes specifically to protect the fiber from the stress of mechanical harvesting. Because ordinary, shorter-staple Egyptian cotton is sold under the same country name, the Cotton Egypt Association runs its own accreditation program, including DNA-based verification, to mark genuine, traceable Giza-grade cotton in a finished product.

Pima is the generic varietal name for extra-long-staple American Gossypium barbadense, with a staple length of roughly 34 to 42mm against about 22 to 28mm for standard upland cotton, and the word itself is not trademarked. Supima is different: it is a registered trademark owned by the American Supima Association, licensed to roughly 600 mills, manufacturers and brands worldwide, and it may legally be used only on products made from 100 percent American-grown Pima cotton that meets the association’s own standards for fiber length, fineness and strength.

From boll to bale

In the United States, every bale of ginned cotton is sampled and classed by the USDA before it can be traded, and that classing measures staple length, strength, micronaire (fineness), color, uniformity and leaf content, all before the bale reaches a mill. Ginning itself is a two-stage mechanical process: the picked cotton is dried and cleaned of leaf trash, then circular saws pull the lint fibers through ribs spaced too narrowly for the seed to pass through, separating fiber from seed before the lint is pressed into bales of roughly 500 pounds.

What mercerization actually changes

Mercerization is often confused with a name like Sea Island or Supima, but they describe two completely different things. English chemist John Mercer discovered in 1844 that treating cotton, or linen, with a strong caustic soda solution and then washing it out shrank the fabric and increased both its tensile strength and its ability to take dye, and he patented the process in 1850 and 1851. The silky sheen now associated with mercerized cotton is a separate refinement, credited to Horace Lowe in 1889, who found that holding the fabric under tension during the caustic treatment produced that lustrous finish. Mercerization can be applied to any cotton yarn, long-staple or not. A short-staple, unremarkable cotton can be mercerized and take on that sheen, and a genuine Sea Island cotton can be left unmercerized. The two labels answer different questions: which raw cotton went into the yarn, and how that yarn was finished afterward.

On a shirting label, the yarn count tells you a third, separate thing: how fine the spun thread itself is. A higher number such as “100s” or “140s” means a finer single yarn spun from the same weight of fiber, and a fraction like “100/2” means the yarn is two-ply, two single yarns of that fineness twisted together, which typically adds strength and reduces pilling compared with an equally fine single-ply yarn. This counting system, English cotton count, is described in the National Cotton Council’s own reference material and is an established ASTM standard.

Sources

1. Britannica, “Cotton: Description, Fiber, History, Production, Uses, Botanical Name, and Facts”, accessed 2026-09-25.
2. Frontiers in Bioengineering and Biotechnology, review article on cotton fiber cellulose content, 2024, accessed 2026-09-25.
3. Wikipedia, “Staple (textiles)”, accessed 2026-09-25.
4. National Cotton Council, “Cotton: From Field to Fabric, Ginning”, accessed 2026-09-25.
5. National Cotton Council, “Cotton: From Field to Fabric, Yarn Production”, accessed 2026-09-25.
6. West Indian Sea Island Cotton Association (WISICA), “The Story of Sea Island Cotton”, accessed 2026-09-25.
7. gizacotton.com, “The origin of Egyptian Cotton”, accessed 2026-09-25.
8. Cotton Egypt Association, “Egyptian Cotton Accreditation Procedure”, accessed 2026-09-25.
9. Supima, “FAQ”, accessed 2026-09-25.
10. Wikipedia, “John Mercer (scientist)”, accessed 2026-09-25.
11. Wikipedia, “Mercerisation”, accessed 2026-09-25.