Xiamen Unitex Trade Co., Ltd. is a professional underwear sourcing & supply-chain management company based in Xiamen, Fujian Province, in the Xiamen–Quanzhou–Jinjiang knitwear cluster of south-east China. Founded by Will Lin, who has worked in the apparel trade since 2004, the company has been exporting since 2009 and was incorporated in Xiamen in 2013. It runs its own liaison office in Jinjiang and works with a network of BSCI & OEKO-TEX Standard 100 certified partner factories to serve retailers and brands across Europe, the US and Australia.
Cotton is the fibre most often claimed and least often verified in an underwear programme. A label that reads 100% cotton is a statement about fibre content, and fibre content is measurable: it can be checked by hand on a sample, and it can be settled definitively by a laboratory test. Between those two lies everything a buyer actually needs — a way to reject an obviously wrong sample before spending money on testing, and a standard to put into the purchase order so the dispute never arises.
What “100% cotton” means on a specification sheet
On a specification sheet, 100% cotton is a fibre-content declaration, not a quality grade. It says nothing about yarn count, fabric weight, shrinkage or colour fastness, and two fabrics both correctly declared as 100% cotton can behave completely differently in a wash test.
That gap is where mislabelling lives. A fabric blended with polyester and sold as pure cotton usually shows itself in the hand and in the wash, which is why the checks below are worth running on every new sample rather than trusting the label. Where the sample passes the hand checks but the price sits well below the market for combed cotton, ask for a fibre-content test report before approving bulk.
Cotton’s measured properties are the reference point for all of this. The fibre absorbs 8–10 per cent of its own weight in moisture at normal humidity, tolerates drying and dyeing below about 110 °C without damage, and resists alkali — which is why cotton takes reactive dye so well and why it can be washed with strong detergents without losing strength. Its weaknesses are equally measurable: shrinkage of 2–5 per cent unless the fabric is pre-shrunk, creasing, and no elastic recovery of its own.
Test 1: hand and elastic recovery
Stretch a small section of the fabric and release it. Cotton has a slightly astringent, substantial hand and recovers slowly, leaving a soft crease; a polyester-rich fabric feels smoother, stretches further and springs back almost instantly.
Two further checks confirm the impression. Rub the cut edge — cotton throws up short fibres of visibly uneven length, while a synthetic edge stays uniform. Then crush the fabric in your fist, hold it for a few seconds and open your hand: the deeper and more persistent the creases, the higher the cotton content.
None of these is a measurement. They are a screening step, and their value is that they cost nothing and take a minute.
Test 2: how the fabric reflects light
Hold the fabric at roughly 45 degrees to a light source and look along the surface. Unless it has been mercerised — which gives cotton a deliberate lustre — cotton reflects softly and reads slightly matte, while a synthetic-rich fabric throws a harder highlight.
Brightness is a second signal. Optical brighteners make white polyester look whiter than white cotton, sometimes to the point of looking bluish under office lighting. Compare the sample against a known cotton white rather than judging it on its own.
Test 3: water absorption
Place a drop of water on the surface and time how it spreads. Cotton wicks immediately and the wet area darkens; a fabric with a high synthetic content holds the drop on the surface longer and spreads it more slowly.
For underwear this is the test that matters most in use, because absorption is what a comfort claim rests on. A fabric that passes the hand checks but beads water will not perform as cotton in wear, whatever the label says.
Test 4: the burn test, and where it stops being conclusive
Pull a few yarns from a seam allowance — not from the sewing thread, which is usually cotton regardless of the shell fabric — and burn them over a heatproof surface. Cotton burns like paper: a yellow flame, a smell of burning paper, and grey-white ash that crumbles between the fingers, with no melting and no bead.
Polyester behaves in the opposite way: it melts and drips, gives off black smoke and a smell of hot plastic, and leaves a hard black bead that will not crush. Blends fall between the two, and that is the limit of the method — a 90/10 blend and a 70/30 blend both burn with a mixed result, and neither can be quantified by eye.
The burn test is a screening tool, not a certificate. It is also a fire risk, so work with a single yarn in a ventilated area rather than on a finished garment.
Lab verification: what to ask the mill for
Fibre content is quantified in a laboratory by chemical dissolution, under the ISO 1833 series. A sample is weighed, the components are dissolved selectively, and the residue is weighed again; the result is a percentage per fibre, reported to a stated tolerance. That report is the only document that settles a fibre-content dispute, and it is cheap relative to the cost of a rejected bulk order.
Ask for three things with it: the test report itself, the colour-fastness results under ISO 105 (washing, rubbing and perspiration are the three that matter for underwear), and the shrinkage figures from the pre-shrunk finish. Together they describe the fabric well enough to write a specification that a factory can be held to.
Where cotton fails in underwear, and how blends fix it
Cotton’s weaknesses show up in exactly the places underwear is judged: it creases, it shrinks 2–5 per cent unless pre-shrunk, and it has no elastic recovery, so a waistband made of cotton alone bags out.
The standard answer is a blend rather than a different fibre. Adding 5–10 per cent elastane restores recovery at the waistband and leg openings without changing the hand of the fabric much, and a cotton–modal blend improves drape and reduces the creasing that shows through outer clothing. Both remain majority-cotton fabrics; both need their fibre content declared accurately, which brings the discussion back to the specification.
What does not work is accepting a blend at a pure-cotton price. If the quotation for a 100% cotton programme sits materially below the market for the same yarn count and weight, the difference is usually in the fibre, not in the margin.
What to write into the purchase order
Put the measurable items in the order, not in an email. A specification that a factory can be held to carries five lines:
- Fibre content, with the fibre names exactly as they will appear on the care label.
- Fabric weight in g/m², and the knit or weave.
- Shrinkage limit after the specified wash cycle.
- Colour-fastness standard, quoting the ISO 105 parts that apply.
- Custom logo position on the care label and waistband, with the artwork reference.
Add the inspection standard — AQL under ISO 2859-1 — and the sampling plan for the fibre-content test. Those two lines are what turn the specification into something enforceable at final inspection.
Once those are in the order, the hand tests and the burn test become what they should be: a way to catch a problem early, not an argument to have after the container has shipped.
Partner factories in our network hold amfori BSCI and OEKO-TEX Standard 100 certification. Send a sample and the specification you intend to order against, and the fabric can be checked against both before a bulk commitment is made.
· Xiamen Unitex Trade Co., Ltd. — OEM & ODM underwear sourcing partner