A factory emails you a quote: "12 oz natural cotton canvas, $4.80/yd." You write back, "great, let's sample." Eight weeks later the sample arrives and it feels thin, stiff, and rough. Not what you pictured.
The quote wasn't wrong. It just wasn't specific enough to describe the product. A complete fabric spec sheet has seven fields. This article is what each one means and what to push back on when something's missing.
Field 1 — Fiber composition
The easy one. "100% cotton," "60/40 cotton-polyester," "95% cotton, 5% spandex." On a quote this should include the specific type of each fiber:
- Cotton: combed vs carded (combed is smoother and more expensive), organic vs conventional, long-staple (Pima, Egyptian) vs standard
- Polyester: virgin vs recycled (GRS-certified), standard denier vs micro-fiber
- Wool: merino (fine, 17–23 micron) vs lambswool vs coarse wool
- Viscose family: viscose vs modal vs Tencel/lyocell — all cellulosic, very different sustainability and drape profiles
If the spec just says "cotton," ask "combed or carded, staple length?"
Field 2 — Weight (GSM or OSY)
GSM — grams per square meter — is the universal unit. Heavier fabric = higher GSM.
Reference points by product type:
- T-shirts: 140–200 GSM (lighter = more drape but wears out faster; heavier = more durable, boxier silhouette)
- Hoodies / sweatshirts: 280–420 GSM French terry or fleece
- Canvas bags: 280–550 GSM (10oz ≈ 340, 12oz ≈ 407, 16oz ≈ 542)
- Button-down shirts: 110–180 GSM poplin or oxford
- Denim: 230–450 GSM (8oz lightweight, 14oz+ heavy "raw" denim)
A spec sheet should state GSM with a tolerance (usually ±5%). The weight you approve in the sample is the weight the bulk run needs to hit.
Field 3 — Weave or knit structure
Woven fabrics: plain weave, twill (diagonal lines, drapes heavier), satin (one side smooth, other side matte), oxford (small basketweave), canvas (heavy plain weave), poplin (fine plain weave).
Knit fabrics: jersey (single knit, lightweight), interlock (double knit, thicker and more stable), rib (vertical lines, stretches horizontally), French terry (loops on back, smooth face), fleece (brushed back for warmth).
Why it matters: A 180 GSM jersey and a 180 GSM interlock are the same weight but feel entirely different. The interlock is more stable, less prone to curling, and drapes heavier. On a spec sheet you want both weight and structure called out.
Field 4 — Yarn count
Yarn count is a measurement of yarn fineness. Higher number = finer yarn = softer, smoother, more expensive fabric.
The common systems:
- Ne (English cotton count): higher is finer. 20s is coarse (canvas), 30s is standard (mid-weight apparel), 40s is fine (dress shirts, fine tees), 60s+ is very fine (luxury shirting)
- Denier (for filament fibers like polyester): lower is finer. 40 denier is very fine (hosiery), 70 denier is standard (dress apparel), 420 denier is heavy (performance bags, workwear)
- Tex: metric equivalent, mostly used for technical fabrics
On a cotton fabric the single biggest lever on hand-feel is yarn count. Same GSM, 20s vs 40s, completely different products.
Field 5 — Shrinkage
Two numbers: lengthwise and widthwise. Usually stated as percentages after a standard wash test (AATCC 135 in the US, ISO 5077 internationally).
What's acceptable depends on construction and use case:
- Pre-shrunk cotton: 3–5% expected (factory has washed the fabric before cutting; remaining shrinkage is minor)
- Non-shrunk cotton: 5–10% (fabric will shrink dramatically on first home wash; sizes must be cut oversized to compensate)
- Polyester: under 1%
- Wool: extremely variable; worsted wool 1–3%, woven wool 3–5%, felted wool can be 10%+
If a factory quotes fabric without stating shrinkage, they likely haven't tested it. Ask for a test report.
Field 6 — Colorfastness
Three numbers:
- Wash fastness (ISO 105-C06): graded 1–5, with 5 being "no visible color change." Look for ≥4 for white or light colors.
- Light fastness (ISO 105-B02): graded 1–8. 6+ for outdoor products, 4+ acceptable indoors.
- Rub fastness / crocking (ISO 105-X12): dry and wet rub separately, graded 1–5. ≥4 is what you want for anything that sits against skin or other surfaces.
A spec sheet that claims "colorfast" without citing the test is making a marketing claim. A proper spec sheet lists the test name and the grade.
Field 7 — Chemistry certification
At a minimum, for anything sold into the EU or touching skin: OEKO-TEX Standard 100. This tests for ~350 restricted substances across 4 categories (infant / direct skin contact / non-direct skin / decoration). Tells you the finished fabric doesn't contain harmful residue.
Beyond that:
- GOTS — if the fiber is organic and the claim extends to processing
- GRS / RCS — if the fiber is recycled
- bluesign® — process-level certification covering chemistry, water, energy, and worker safety at the mill
- ZDHC MRSL — the industry-aligned restricted substances list that most major brands' suppliers are held to
A quote without any chemistry certification mentioned is fine for internal/casual products; for anything brand-forward or EU-bound you want at least OEKO-TEX.
What a complete spec sheet looks like
A real factory spec sheet for "12 oz natural cotton canvas" should read something like:
Cotton canvas, 100% organic cotton (GOTS in-conversion)
- 407 GSM (12 oz/sq yd), ±5%
- Plain weave, 2/1 twill
- Yarn count: warp 10s, weft 7s
- Shrinkage: 3.5% length, 3.0% width (pre-washed, AATCC 135)
- Wash fastness: grade 4–5
- Light fastness: grade 6
- Rub fastness: grade 4–5 dry, 3–4 wet
- OEKO-TEX Standard 100 certified (class 2)
That's a product. "12 oz canvas, $4.80/yd" is a headline.
Frequently asked questions about fabric spec sheets
What's the difference between GSM and ounces per square yard?
GSM (grams per square meter) is the metric convention used by most of the world's mills. OSY (ounces per square yard) is used in the US. Conversion: 1 oz/sq yd ≈ 33.9 GSM. A "12 oz canvas" is roughly 407 GSM; a "180 GSM jersey" is roughly 5.3 oz/sq yd. Mills will quote in their native unit — know how to convert or ask them to restate in yours.
What shrinkage percentage should I expect?
Industry norms: cotton jersey 5–8%, cotton canvas 3–5%, polyester/cotton blend 2–4%, pure polyester <1%. A spec sheet should state both length and width shrinkage separately (they're usually different). If the factory claims "pre-shrunk" they should be able to produce a test report from a third-party lab (usually SGS, Bureau Veritas, or Intertek).
Do I need OEKO-TEX on every product?
Probably not, but yes for anything that touches skin extensively (base layers, kids' wear, bedding) or for any product sold into the EU where the chemistry-restriction list is stringent. OEKO-TEX Standard 100 is the baseline certification — tests for ~350 restricted substances. STeP is the facility-level environmental+social addition. For promotional totes that live in someone's trunk, OEKO-TEX adds cost for a claim few customers care about.
Can I substitute yarn count or GSM to lower cost?
Yes, but understand what you lose. Dropping from a 30s yarn count to a 20s yarn count (coarser) saves 8–15% on fiber cost but the fabric feels noticeably rougher. Dropping from 180 GSM to 160 GSM saves similarly but the fabric drapes flimsier and wears out faster. For bulk promotional products the tradeoff often works; for brand-forward apparel it usually doesn't.
Related reading
- GOTS vs "Organic Cotton": What's Actually Certified — if your fiber is organic cotton, what does that actually guarantee end-to-end.
- Recycled Polyester (rPET): The Honest Ledger — the rPET-specific version of the certification question.
- Writing a Tech Pack: What Factories Actually Need — where fabric spec fits into the broader production blueprint.
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