Reading a Fabric Spec: GSM, Yarn Count, Construction and Dye Method

This is not a fabric dictionary. It is the thing that actually decides your product: how to write a fabric specification, so the mill quotes against your line rather than you accepting whatever the mill offers. Every field below moves cost, hand-feel or failure rate, and a mill quoting against a partial spec will assume the cheapest option on every field you leave blank. It sits inside sourcing apparel direct from factories and feeds directly into the bill of materials in a tech pack.

Where this page sits. It answers one question — how to read a fabric spec, and then how to write one — field by field. Four sibling pages carry the depth on the individual fields, and you will want them open alongside this one. For the weight number itself, every value and its ounce equivalent, use the GSM fabric weight chart with oz/yd² equivalents. For the yarn — carded and combed, ring-spun and open-end, and what each does to hand-feel and price — use combed ring-spun cotton explained. For the dye field, garment dye vs piece dye vs yarn dye compares the three stages on minimum, consistency and cost. And for buying the cloth itself — mills, converters, jobbers and fabric minimums — use fabric sourcing for brands. This page is the spec line; those four are the fields inside it.

The seven fields a complete fabric specification line contains

A usable spec names all of these, in this order:

1. Fibre content by percentage, descending — "100% cotton", "95% cotton / 5% elastane"
2. Structure — single jersey, piqué, 1×1 rib, interlock, brushed loopback fleece
3. Yarn count in Ne — 20s, 30s, 40s
4. Spinning and preparation — open-end, ring-spun, compact; carded or combed
5. GSM, stated as finished, with a tolerance
6. Dye method and dye class — reactive piece-dyed, pigment garment-dyed, yarn-dyed
7. Finish and performance tolerances — compacted, softened, shrinkage, spirality, colourfastness

Leave out field 4 and you get open-end carded. Leave out "finished" on field 5 and you may get greige weight. Leave out "compacted" and you get fabric that meets your GSM and fails your shrinkage test.

Knit structures and why single jersey, piqué, rib and interlock behave differently

Structure is decided by how many needle beds the machine uses, and it determines curl, stretch and stability before any other variable.

Single knits (one needle bed):

• Single jersey — the tee fabric. It curls at cut edges: the bottom edge curls to the back, the side edges to the front. Width extensibility is roughly twice its length extensibility. It is prone to spirality, the residual yarn twist that rotates side seams after washing.
• Piqué — a knit and tuck combination producing micro-mesh holes. This is the polo fabric. Less curl and less stretch than jersey, more breathable.
• French terry — uncut float loops on the back, good stretch retention. Sweats and layering.
• Fleece (2-end / 3-end) — the same loops napped or brushed on the inside for insulation. Heavier.

Double knits (two needle beds):

• Rib (1×1, 2×2) — does not curl, and has roughly double the width extensibility of single jersey. That single property is why rib is used for necks, cuffs and waistbands: it has to stretch over a head or a hand and recover. 2×2 has deeper wales and more recovery bulk than 1×1.
• Interlock — needles directly opposed, two feeds per visible course. Very stable, does not curl, smooth on both faces, less stretch than rib. Baby clothes, turtlenecks and quality basics.
• Ponte di Roma — a heavier interlock variant, usually with elastane, for tailored knit trousers and jackets.
• Thermal / waffle — cellular pockets; grows in width and shrinks in length. Base layers.

The practical consequence: if your neck rib is stretching out in wear, the fault is usually the rib specification, not the sewing operation.

GSM benchmarks by fabric, and the oz/yd² conversion trap

Knit fabric weights by end use. GSM is grams per square metre on finished fabric.

Two traps live in this table.

The conversion trap. US vendors quote oz/yd²; Asian mills quote gsm. 1 oz/yd² ≈ 33.9 g/m². So:

• 4.3 oz × 33.9 = 146 gsm — a lightweight tee
• 5.3 oz × 33.9 = 180 gsm — a premium tee
• 6.0 oz × 33.9 = 203 gsm — a "heavyweight" retail tee

Two quotes, one in ounces and one in grams, are not comparable until you convert. Convert everything to gsm in your own documents and never let both units coexist in one spec.

The greige trap. GSM is measured on finished, relaxed, conditioned fabric. Greige (undyed, unfinished) and finished GSM differ by 5–15%, because dyeing, compacting and softening all change the fabric. A quote for "180 gsm" that turns out to be greige is a different fabric from the one you specified. Write "180 gsm finished, ±5%" and require the mill to state its test conditions. Conditioning before measurement is standardised at 20°C and 65% relative humidity for at least 24 hours under ASTM D1776 / ISO 139.

Worked example: what 40 gsm costs you per unit

A 180 gsm cotton jersey tee consumes about 0.27 kg of finished fabric including roughly 10% cutting wastage, at a finished dyed fabric price of about $8.15/kg, which is $2.20 of fabric in a roughly $4.30 FOB tee — 51% of FOB. Scale that linearly with weight:

Fabric weight and fabric cost per tee at three GSM specs, on a finished dyed jersey basis.

Moving from 160 gsm to 200 gsm adds $0.49 per unit at the mill, about 11% of a $4.30 FOB. Then duty applies on top: at the August 2026 all-in rate of 26.5% for a cotton knit tee from India or Bangladesh (16.5% MFN plus the 10% Section 301 forced-labor layer), that $0.49 becomes $0.62 landed before freight. Verify current rates against the HTSUS before relying on any figure; see US import duty on clothing in 2026. Across a 10,000-piece order that is $6,200 of landed cost bought with one line of a fabric spec, which is why GSM is a merchandising decision rather than a technical detail.

Mills quote fabric on two different bases, and the two are not comparable

Before you compare fabric prices per kilo, establish what the quote covers. A mill can quote you finished dyed fabric per kilogram, which is knitted, dyed, finished cloth ready for the cutting room, or it can quote you yarn plus a separate conversion charge for knitting, dyeing and finishing. Both are normal, and neither is disclosed unless you ask.

The consequence is that a $5.50/kg quote and an $8.15/kg quote can describe exactly the same fabric — the first on a yarn basis with conversion still to be added, the second all-in. This is one of the most common costing errors in apparel: a cost sheet built on a yarn-basis number silently omits conversion, and on those two figures the fabric line comes in about a third light against the invoice. Ask which basis the quote is on, get it in writing on the quotation, and restate every mill's number on the same basis before you compare them. The $8.15/kg used in the worked example above is a finished dyed price.

Yarn spinning: open-end, ring-spun and compact

Spinning methods and what they cost. Cost is expressed relative to open-end as the baseline.

If a tee quote comes in noticeably below the market and the spec does not say ring-spun, it is open-end. That is a legitimate choice for a promotional programme and the wrong choice for a $45 retail tee, because the hand-feel difference is immediately obvious to a customer.

Carded versus combed, and why "combed ring-spun" is the standard premium tee spec

Carding and combing are a separate axis from spinning method, and they apply to any spinning method. Carded yarn goes straight from carding to spinning. Combed yarn passes through an additional combing step that removes short fibres, the noil, typically 12–20% of the fibre by weight, leaving longer and more parallel fibres.

The result is smoother, stronger, less prone to pilling, and more expensive, because you have thrown away up to a fifth of the raw material before spinning. That combination, "combed ring-spun", is the standard premium tee specification: it names the preparation and the spinning method, and it is the two-word phrase that separates a retail tee from a giveaway tee.

You can also buy carded ring-spun (cheaper, still smooth) or combed open-end (rare, and largely pointless). Name both axes explicitly and you remove the ambiguity.

Yarn count in Ne, and how it interacts with GSM

Yarn count in apparel cotton is expressed in Ne, the English cotton count. Higher Ne means finer yarn.

• 20s — coarse, heavy jersey
• 30s — the standard tee count
• 40s — fine, lightweight
• 50s–60s — fine shirting and luxury knits

Count and GSM are independent, and this is where specs go wrong. A 180 gsm fabric knitted from 30s is denser and smoother than a 180 gsm knitted from 20s, because finer yarn needs more loops per unit area to reach the same weight. Two mills can both deliver "180 gsm single jersey" and produce visibly different fabrics. Specify both numbers or you have specified neither.

Dyeing methods: yarn dye, piece dye and garment dye

Dye method by stage, minimum, consistency and cost. Minimums are per colour and are the binding constraint on how many colourways a range can carry.

Garment dye is the small-run escape hatch: it lets a brand carry six colours on a 1,000-piece programme that could never meet six piece-dye minimums. Above roughly 5,000 pieces, piece dye is up to 25% cheaper. The wider MOQ picture, including the 300–500 kg fabric dye-vessel minimums that actually set your floor, is in dye-lot minimums and MOQ economics.

Dye chemistry: reactive, pigment and disperse

• Reactive dye forms a covalent bond with cellulose. It is the right choice on 100% cotton and other cellulosics: excellent wash and rub fastness, vibrant even shades. It needs hot water, longer cycles and heavy salt and water use, so it costs more.
• Pigment dye is not a dye. Pigment sits on the fabric surface held by a binder resin. Lower temperature, lower cost, lower MOQ, and it works on blends. It fades with washing by design — that is the washed, vintage aesthetic people buy it for — and its wet crocking is weak. Crucially, batch-to-batch shade variation is normal on pigment and must be written into the tolerance rather than treated as a defect. If you specify pigment and then reject lots for shade variation at inspection, you are rejecting the process you bought.
• Disperse dye is for polyester, and needs high temperature and pressure, with sublimation and migration risks on blends.
• Vat and indigo dyes are the denim family.

Whichever you choose, the colour call-out itself has to carry the Pantone code, system and a Delta E tolerance with a named formula. See Pantone codes, lab dips and Delta E.

Chambray fabric, and what changes when the cloth is woven

Everything above is written for knits, because most brands start there. A woven uses the same seven fields with two substitutions: weave replaces knit structure, and thread count — ends per inch × picks per inch joins yarn count and weight as a density measure. Chambray fabric is the most useful worked example, because its defining property sits in the dye field rather than the weave.

Merriam-Webster defines chambray as "a lightweight clothing fabric with colored warp and white filling yarns". A coloured warp crossed with an undyed weft is what produces the pale two-tone surface. That definition carries a hard sourcing consequence: chambray is yarn-dyed by construction. The colour must be in the warp yarn before the cloth is woven, so it sits in the top row of the dye table above — one dye lot per yarn colour, the highest minimum per colour of the three stages, and no option to defer the colour decision the way a piece dye allows. What that costs is set out in garment dye vs piece dye vs yarn dye.

One naming note, because it wastes time on quotations: the same cloth is listed as chambray cotton, cotton chambray, chambray textile, and often enough that mills answer to it, the misspelling chambrey fabric. Those are one fabric, not four.

A cotton chambray fabric spec line takes the same shape as the knit line below, with the woven fields substituted:

Shell: 100% cotton chambray fabric, plain weave, yarn-dyed warp with undyed white filling, [Ne warp × Ne weft], [ends × picks per inch], [weight] gsm finished ±5%, warp shade to [Pantone code and system] at ΔE CMC(2:1) ≤ [tolerance] under D65/10°, [finish], shrinkage ±2% length and width.

The bracketed fields are the ones only you can fill, from your hand-feel benchmark and your target price; a mill quoting against them blank will assume the cheapest option on each, exactly as it does on a knit. Two numbers move when you cross from knit to woven. Shrinkage tolerance tightens from the ±3% norm on cotton knits to ±2% on wovens. And shirting weight is usually quoted in oz/yd² by US vendors, so convert at 33.9 before you compare two mills — the full table is in the GSM fabric weight chart with oz/yd² equivalents.

A complete worked fabric spec line for a premium tee

Everything above, assembled into the form you would put on the bill of materials:

Shell: 100% combed ring-spun cotton single jersey, 30s Ne, 180 gsm finished ±5% (measured relaxed and conditioned per ASTM D1776, 20°C / 65% RH, 24 hrs), reactive piece-dyed, compacted, silicone softened. Colour: PANTONE 19-4052 TCX, tolerance ΔE CMC(2:1) ≤ 1.0 under D65/10°. Shrinkage ±3% length and width after 3 wash cycles per AATCC TM135-3-IV-Ai. Spirality ≤5% per AATCC TM179. Colourfastness to laundering ≥ 4.0 shade change and ≥ 4.0 staining (AATCC TM61); crocking ≥ 4.0 dry, ≥ 3.0 wet (AATCC TM8).

Neck rib: 1×1 rib, 100% combed ring-spun cotton, 30s Ne, 220 gsm finished, dyed to match shell, ΔE CMC(2:1) ≤ 2.0 against the approved shell dip.

That is eleven decisions the mill can no longer make for you: fibre, structure, count, spinning, preparation, weight, weight basis, dye method, dye class, finish and four performance tolerances. Each one of those, left blank, defaults to the cheapest available option.

Two operational notes. First, fabric development has its own calendar: custom dyeing adds 4–8 weeks on top of the 1–4 week fabric sourcing baseline, so the spec must be frozen early. See where fabric development sits in the sampling calendar. Second, the performance tolerances in the spec are exactly what a third-party lab and inspector will measure, which is covered in shrinkage and colourfastness testing at inspection. A tolerance you did not write is a tolerance nobody will test.

Definitions for GSM, greige, Ne, piece dye and interlock are collected in the Yarnstick glossary of sourcing terms.

Frequently asked questions