Fibre Composition Label Rules: Tolerance and Testing
Quick answer
A blend never lands on exactly 50/50. Fibre composition on a label is a declaration with a permitted tolerance around it — typically a small percentage allowance, with stricter treatment for named luxury fibres and a rounding convention for the figures themselves. The practical risk is not that a blend drifts slightly, but that the label, the test report and the customs invoice state three different numbers. The label should be written from a test result, not from the yarn order.
A buyer specifies a 70/30 wool-nylon blend, the spinner delivers to that specification, and the finished garment tests at 68.4 percent wool. Nothing has gone wrong. Blending is a physical process with real variation, which is why every labelling regime includes a tolerance — and why the buyer who understands that tolerance stops treating a two-point difference as a defect and starts treating an inconsistent document set as the real exposure.
Why does a fibre blend drift in production?
Because blending is not a chemical formula. Fibres are weighed, opened, mixed and carded, and the resulting yarn varies around the target for four reasons.
Weighing and mixing variation. Every stage has a tolerance, and small errors at the opening stage become a percentage point or two in the finished yarn. Our notes on sweater yarn explain how a blend is built in the first place.
Fibre loss in processing. Short fibres and dust are removed during carding and combing, and they are not removed in the same proportion from each component. A blend can shift simply because one fibre sheds more waste than the other.
Test method variation. Two labs testing the same yarn can differ by a percentage point depending on the method used to separate the fibres. The number on a test report is itself an estimate.
Yarn substitution. A supplier running short of one component may use a nearby count from a different blend. This is the one cause that is not natural variation, and our notes on yarn substitution explain why it needs written approval.
What does the tolerance actually allow?
Most labelling regimes work on a similar principle: the declared composition must be accurate within a permitted allowance, and the allowance is tighter for certain named fibres.
- A general allowance for manufacturing variation, typically a small percentage — in the region of three percentage points in several major regimes, though the exact figure and its application differ by jurisdiction.
- A stricter allowance for named luxury fibres such as cashmere, wool or silk in some markets, because those names carry commercial weight and consumers pay a premium for them.
- Rounding conventions for how the percentages are expressed — whether they must total exactly 100, how a small component is described, and whether "other fibres" can be used.
- Disclosure thresholds below which a minor component need not be named in some regimes, but must be in others.
The figures vary by market and change over time, so the working rule is to confirm the requirement for the destination rather than to apply one number globally. Our notes on care and composition labelling set out the market-by-market requirements, and this article covers what to do about the tolerance itself.
What is the real risk, if a blend is allowed to drift?
The tolerance protects normal variation. It does not protect inconsistency, and inconsistency is where buyers actually get hurt.
The label written from the yarn order rather than a test. A label saying 70/30 because that is what was ordered, when the yarn tested at 68/32, is a declaration the supplier cannot defend if challenged. Writing the label from a test report is the only defensible route.
Three different numbers on three documents. The label says 70/30, the invoice says 72/28 because the purchase order was amended, and the test report says 68/32. Each number might be individually defensible; together they are a hold at customs and a compliance question.
A luxury fibre claim that fails on test. A garment sold as cashmere-rich that tests below the threshold for the term is not a tolerance issue — it is a misdescription, with consumer-protection exposure. Our notes on cashmere grades cover how the fibre is graded in the first place.
Duty classification shifting. Fibre composition determines the customs heading, so a blend that drifts across a threshold can change the applicable duty rate. Our notes on HS codes explain how composition drives the code.
How should a buyer handle composition in the order?
- Ask for the test report with the bulk, not just at sampling. Fibre composition testing is a standard lab service, and our notes on lab testing cover what else should be tested at the same time.
- Write the label from the tested figure, rounded to the destination's convention, and record the test reference alongside the label artwork.
- Fix one composition string and use it identically on the label, the invoice, the packing list and the declaration.
- Specify the blend as a range rather than a point in the tech pack — 68–72 percent wool, for example — so the factory is not chasing a figure the process cannot hit.
- Treat a named luxury fibre as a claim. If the garment is sold as cashmere, the tested percentage must clear the threshold for that term, and the tolerance will not rescue a shortfall.
- Re-test on a reorder, since a new yarn lot can shift the composition.
Where does the composition string appear?
The same string has to serve four purposes at once: the sewn-in label declares composition to the consumer, the invoice declares it to customs, the test report substantiates it, and the line sheet quotes it commercially.
A difference between any two is a problem of a different kind — a compliance question between label and test report, a customs hold between invoice and label, a consumer description that may not match the goods between line sheet and label. Our notes on shipping documents cover the invoice side, and the line sheet the commercial side.
The discipline is to designate one authoritative string, taken from the test report and rounded to the destination convention, and treat every other document as a copy of it.
What should a supplier do?
A supplier working with export buyers should be able to state the composition of the yarn it used, provide a test report from a recognised lab, and produce a label that matches that report rather than the order sheet. It should also flag a substitution before it happens rather than after, because a component change is exactly the case where the tolerance stops protecting anyone.
The practical test of a supplier is simple: ask for the test report for the last order and check whether the label matches it. A supplier who can produce both, and explain any rounding, is one whose composition declaration can be relied on. Our notes on supplier vetting cover the wider set of questions worth asking.
At YZR Sweaters we work with partner factories holding BSCI, SEDEX and Oeko-Tex certifications, welcome factory audits, and support third-party inspection through firms such as SGS and BV. On composition we test, label from the result, and use one composition string across every document in the shipment.
Want your composition labels backed by test reports rather than the order sheet? Send us the styles and destination markets and we will confirm what each one requires.
Get a free quote Browse our knitwear rangeFrequently asked questions
How much can a fibre blend vary from the label?
Most regimes allow a small manufacturing tolerance, commonly in the region of three percentage points for general fibres, with a tighter allowance for named luxury fibres in some markets. The exact figure and how it applies differ by jurisdiction, so the requirement for the destination should be confirmed rather than assumed. The tolerance covers natural variation, not a component substitution.
Should the label state the ordered composition or the tested one?
The tested one. The label is a declaration about the goods, not about the purchase order, so it should be written from a lab result and rounded to the destination's convention. A label copied from the order sheet is a claim the supplier cannot defend if the yarn tests differently, even when the difference falls inside the allowance.
Does a small composition difference affect duty?
It can. Fibre composition determines the customs subheading, so a blend that drifts across a threshold can move the goods into a different duty rate. That is a separate concern from the labelling tolerance: the label has to be accurate for the consumer, and the customs declaration has to be accurate for the tariff.