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How to Inspect PU Foam Grade Before Accepting Cups
Most bra cup disputes do not start in production. They start at acceptance, when a buyer opens the first carton and discovers that “good quality PU foam” meant something different to them than it did to the factory. The fix is unglamorous but reliable: agree a written acceptance standard before the first pair is moulded, then inspect against that standard instead of against a feeling.
This guide covers how to define foam grade in measurable terms, how to build a sampling plan, and how we control incoming foam at our Dongguan factory.
Why “foam grade” is not a standard term
There is no global grading scale for bra cup foam, and no A/B/C classification that every supplier reads the same way. When a supplier says “grade A foam”, that phrase carries no contractual weight — it is a sales adjective, not a specification.
What does carry weight is a short list of measurable properties. A purchase order that names those properties, states the target range and points to a sealed reference sample gives you something you can inspect against.
Five properties an acceptance standard must define
1. Density
Density drives support, weight and how the cup ages. Our standard PU foam cups sit in the 25-30 kg/m³ range, balancing shape retention against a soft hand feel. It is also the easiest property to verify without a laboratory: cut a clean block from a spare cup, measure it, weigh it, divide mass by volume. The arithmetic and common measuring errors are covered in our article on what PU foam density means for buyers.
2. ILD (indentation load deflection)
ILD describes how firm the foam feels under pressure. Our cups are normally specified at ILD 28-35, which suits everyday bras, bralettes and most moulded lingerie. Sports styles usually sit at the firmer end of that window. ILD cannot be judged by thumb pressure alone, so it belongs in the PO as a number with a tolerance, cross-checked against a sealed sample. Our explanation of ILD and rebound behaviour covers how to read the figure correctly.
3. Yellowing resistance
Foam yellows through UV exposure, heat and contact with phenolic packaging. Our cups are supplied at 4-grade yellowing resistance on the 1-5 grey scale, the practical requirement for white and pastel garments shipped to Europe and North America. This is separate from certification: OEKO-TEX Standard 100 governs harmful substance limits and GRS governs recycled content. Neither is a yellowing test, and any supplier presenting them as one is confusing two different things.
4. Dimensional consistency
Cup height, wing width and depth need a defined tolerance, but a drawing dimension is a poor reference for a moulded soft-goods part. Define tolerance against a sealed reference sample that both sides sign and retain — one pair in your office, one at the factory.
5. Appearance and workmanship
This is where subjective disputes concentrate, so write it down in advance: acceptable surface marking, edge finish, mould line visibility, colour shade variation between lots, and airflow hole placement. Photograph both an accepted and a rejected example and attach both to the PO.
Build a sampling plan before the first shipment
An acceptance standard without a sampling plan is only half a system. Three decisions need making.
- Define the lot. One production batch, one style, one colour, one size run. Mixing sizes into a single lot makes any rejection ambiguous.
- Set the sample size. Most lingerie buyers work to ISO 2859-1 (equivalent to ANSI/ASQ Z1.4) general level II, AQL 2.5 major and 4.0 minor. Both sides then know what a pass means.
- Split destructive from non-destructive checks. Density testing destroys the sample, so take those pieces from a small separate allowance and agree who pays for them.
| Check | Method | Where it happens |
|---|---|---|
| Density | Cut, measure, weigh, calculate kg/m³ | Destructive, small allowance |
| ILD | Instrumented indentation test | Certified third-party laboratory |
| Yellowing | Accelerated ageing, graded on grey scale | Certified third-party laboratory |
| Dimensions | Compare against sealed sample | Non-destructive, in-line or at receipt |
| Appearance | Visual against photo standard | Non-destructive, AQL sample |
For the two laboratory items, buyers who need documentary evidence send samples to an accredited testing house of their choosing. We support that process and supply the material information required, and we recommend it whenever a retail customer wants a certificate rather than a supplier statement.
How we control foam before it reaches the press
Acceptance is easier when the upstream control is real. Incoming PU foam is checked against the agreed density and hardness specification on receipt, and any lot outside the window is set aside rather than run. During production, every shift completes a parameter record covering hot-press temperature (160-200°C), pressure (15-30 tonnes) and dwell time (8-15 seconds) for each mould in use.
Those records are what make traceability meaningful. If a complaint arrives six weeks after shipment, we can identify the shift, the mould and the parameter set behind that batch instead of guessing. Finished-goods yield runs consistently above 95%, and our ISO 9001 system exists to keep those records disciplined rather than decorative. The cup profiles this process runs are on our products page.
An acceptance clause you can adapt
Something in the shape of the following, agreed in writing before sampling starts, removes most later ambiguity:
Material: moulded PU foam cup. Density 25-30 kg/m³. ILD 28-35. Yellowing resistance grade 4 minimum on the 1-5 grey scale. Colour, dimensions, edge finish and airflow hole configuration to match the sealed reference sample dated [date], one copy held by each party. Inspection to ISO 2859-1 level II, AQL 2.5 major / 4.0 minor. Density verified by buyer on a three-piece destructive allowance per lot. Supplier to retain production parameter records for each shift for a minimum of twelve months.
Common rejection reasons and their usual causes
| Symptom at receipt | Most likely cause | Prevention |
|---|---|---|
| Softer than the approved sample | Foam lot below the density or ILD window | State both figures in the PO, verify incoming lots |
| Cup height varies across the carton | Sizes mixed in one lot, or mould changed mid-run | Define the lot narrowly, log the mould per shift |
| Yellow cast on white cups | Phenolic packaging or light exposure in transit | Specify grade 4 and non-phenolic packaging |
| Surface marks or visible mould lines | No agreed appearance standard | Attach accepted and rejected reference photos |
| Slow recovery after compression | Over-compressed packing, or foam out of spec | Allow recovery time, then verify density |
That last row matters more than buyers expect. Cups compressed in transit need time to recover their profile, so judging a shipment within minutes of unpacking produces false rejections. Give the cartons a few hours in a normal room before measuring.
Frequently asked questions
Is there an official grading system for bra cup foam?
No. There is no recognised A/B/C scale. Specify density, ILD, yellowing resistance and a sealed reference sample instead — those are the properties that can be measured and disputed on evidence.
Can I verify foam density myself without a laboratory?
Yes. Cut a clean rectangular block from a spare cup, measure its three dimensions in centimetres, weigh it in grams and convert to kg/m³. Cut squarely and use a scale accurate to 0.1 g, since a sloppy cut is the usual source of error.
Does Senfeng issue its own test reports?
We supply material specifications and our per-shift production parameter records. Formal ILD and yellowing certificates come from accredited third-party laboratories, and we recommend buyers commission those directly so the report belongs to them.
What AQL level should I use for bra cups?
ISO 2859-1 general level II with AQL 2.5 major and 4.0 minor is the common lingerie setting. Tighten it for a premium retail programme, but agree the level before production rather than after a problem.
How fast can I get a sample to write my acceptance standard against?
From our library of 2000+ existing moulds, 1-2 working days; a new mould takes 3-7 days. Minimum order is 500 pairs, and we have exported for eight years with no bad-debt record and Sinosure coverage in place.
Setting up a new programme? Send us your target garment, the support level you need and any retail testing requirements. We will propose a specification, produce a sample to seal as your reference, and give you a written acceptance standard to inspect against from the first shipment onward.
Contact us directly: WhatsApp +86 137 1289 0858 | Website: sf-bracup.com
