Cotton Fabric Explained: Weaves, Weights and How to Specify

“Cotton” is not a fabric. It is a fibre that gets spun, woven or knitted into dozens of cloths that share almost nothing except their origin. A cotton voile and a cotton canvas are both 100% cotton, and they have less in common with each other than either has with a synthetic chosen for the same job.

That is why fabric specifications written as “100% cotton” fail. This guide sets out the weave families, the fabric names you will actually meet, the two weight systems and how to convert between them, what yarn count tells you, and the finishing and shrinkage questions that decide whether a delivered fabric behaves like the sample.

Three tiers of confidence:

• Standard — a fixed unit relationship or a published test method.
• Convention — a trade name or a grade with no governing standard behind it.
• Verify required — mill-dependent; confirm on a test report for the specific fabric.

Almost all confusion about cotton fabric comes from mixing up three independent axes:

• Fibre — cotton, and its staple length and grade.
• Construction — how the yarn was interlaced or looped: the weave or knit.
• Finish — what was done to it afterwards: mercerising, sanforising, brushing, dyeing, printing.

A fabric name usually describes the second axis with a bit of the third mixed in, and says nothing about the first. “Mercerised poplin” and “mercerised jersey” are both valid, because mercerising is a finish that can be applied to either construction — but it is not itself a fabric type, and it is a category error to list it alongside poplin and piqué.

Woven cotton comes from a small number of fundamental structures. Everything with a name — poplin, denim, sateen, canvas — is a variation on one of them.

Two corrections worth carrying into any specification. First, “percale” is not a weave family — it is a plain weave, and the name denotes a plain-woven sheeting at a given yarn count and finish. Second, there is no such thing as “the four cotton weaves”. The families are plain, twill, satin and leno; percale sits inside the first, and jersey is not a weave at all.

These are the names you will meet on a spec sheet or a pattern envelope. GSM ranges overlap between suppliers, so treat them as bands and always confirm against a physical swatch.

Knits are loops rather than interlacings, and they behave differently on every axis: more stretch, more air, and more relaxation shrinkage after washing.

Two T-shirts at 140 gsm and 200 gsm are both “100% cotton jersey”, and the second will outlast the first. Within a construction, weight is the buying signal.

Cotton yarn thickness is quoted in the cotton count (Ne) system: the number of 840-yard hanks per pound. A higher Ne means a finer yarn — the opposite direction to Tex.

The conversion is fixed, so it is safe to write into a specification:

• Tex ≈ 590.5 / Ne
• Ne ≈ 590.5 / Tex

Combed cotton yarns for shirting and poplin commonly fall in the Ne 20 to Ne 60 range; coarser counts go into canvas and heavy twill. Two fabrics at the same GSM can be built from very different counts — a coarse yarn in an open weave versus a fine yarn densely packed — and they will not perform the same way.

Fabric weight is quoted either in grams per square metre (GSM) or, particularly for denim and canvas, in ounces per square yard. The conversion is fixed:

• GSM ≈ oz/yd² × 33.9

So 8 oz denim is roughly 271 gsm, 10 oz is about 339 gsm, and 12 oz about 407 gsm. Denim is still quoted in ounces by convention even in markets that otherwise use metric, so the conversion is worth having to hand.

A specification that says “100% cotton” says nothing about any of these. A specification that says “combed ring-spun, Ne 40” tells a mill exactly what to make.

Finish is where a fabric acquires the properties the buyer actually notices:

• Mercerising — treatment with concentrated caustic soda under tension. Swells the fibre, raises lustre and dye uptake, and adds strength. It is a finish, not a fabric type.
• Sanforising — mechanical pre-shrinking. Fabric treated this way is typically held to shrinkage of about 1% or less, against the 2–5% an untreated cotton will move on first wash.
• Brushing / napping — raises the surface to make flannel and fleece.
• Enzyme and stone washing — softens hand and, on denim, produces the worn appearance.
• Compacting — controls relaxation shrinkage in knits.

If repeat orders are behaving differently, the finish is one of the first things to compare after construction and weight.

Cotton shrinks. Unfinished fabric typically moves 2–5% on first wash, most of it in the first cycle. The practical controls are:

• Specify the finish — sanforised or compacted, with a stated shrinkage limit.
• State the test method — the AATCC 135 and ISO 6330 series cover dimensional change in domestic laundering. Naming the method removes the argument about how the figure was obtained.
• Specify in both directions — warp and weft, or length and width for knits. A fabric that shrinks 1% one way and 4% the other will distort a garment even if the average looks acceptable.
• Pre-wash in production where it matters — for garments that must not move in service, the fabric is washed before cutting.

Note that knits relax as well as shrink: a jersey can change shape after washing in a way that is not captured by a simple shrinkage percentage, which is why relaxation is assessed separately.

Confirm the current version and scope of each method before citing it in a contract; this guide names the series normally used and is not a substitute for the published documents.

The items that most often get missed on a first cotton fabric order:

• Construction — the weave or knit family, and the named fabric if there is one.
• Fibre content with blend ratio and tolerance, plus staple grade if it matters.
• Yarn count — Ne, and whether combed and ring-spun.
• Weight — GSM, with the tolerance, or oz/yd² if denim.
• Width and usable width — and whether the quoted width includes the selvedge.
• Finish — mercerised, sanforised, brushed, washed, and to what specification.
• Shrinkage limit in both directions, with the test method named.
• Colour fastness ratings to washing, rubbing and light, with methods and minimum grades.
• Shade standard and dye-lot control — a physical reference and a stated tolerance.
• Retained sample — a labelled cutting from the approved lot, kept under the same conditions as the bulk.

No — it is a fibre. The fabric depends on how it is spun, woven or knitted and how it is finished. A cotton voile at 70 gsm and a cotton canvas at 400 gsm are both 100% cotton and behave nothing alike, which is why a specification that stops at the fibre content is not a specification.

Both are plain weaves used for shirting, and suppliers use the names loosely. Poplin traditionally carries a fine crosswise rib because the weft is heavier than the warp; broadcloth is denser and finer with a slight sheen. In practice the GSM and the hand matter more than the name — compare swatches.

Multiply ounces per square yard by 33.9. So 8 oz is roughly 271 gsm, 10 oz about 339 gsm and 12 oz about 407 gsm. Denim is quoted in ounces by convention even in metric markets.

Because the warp and weft are under different tension during weaving and finishing, and they relax differently. This is normal, and it is why a shrinkage limit should be stated for both directions rather than as a single figure — a fabric at 1% by 4% will distort a garment even though the average looks fine.

The fabric has been mechanically pre-shrunk. Sanforised cotton is typically held to around 1% shrinkage or less, against the 2–5% an untreated cotton moves on first wash. It costs more and it is worth specifying wherever a garment must hold its size.

No — mercerising is a finish applied to cotton to raise lustre, strength and dye uptake. It can be applied to poplin, jersey or any other cotton construction, so it belongs on the finish line of a specification, not on the fabric-type line.

Compare construction first, then yarn count and spinning method, then finish. A change from ring-spun to open-end yarn, or a combed yarn to a carded one, produces a noticeably different fabric at identical fibre content and GSM. Check the retained sample from the approved lot side by side with the new delivery.

Fabric names and GSM bands in this guide are trade conventions with overlapping ranges between suppliers; yarn count, GSM and ounce conversions are fixed relationships. Shrinkage, pilling and fastness figures are mill-dependent — confirm them on a test report for the specific fabric and against a retained sample before ordering at volume.

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