Swim: the chemistry the garment has to survive

The second style on the same purchase order

SW-6208, a one-piece swimsuit. 4,200 pieces, two colours, Black and Almond. Price EUR 8.90 on FOB terms, which means the factory delivers the goods loaded on the ship. Same buyer, same factory, same season.

It is a simpler garment than the bra. Fewer components, a shorter size range, one axis. It is also the one that came back.

In season two, Aubrette deducted a quality claim of EUR 6,900 against SW-6208. The leg and strap openings on those suits had gone slack after a summer's use. Aubrette's own laboratory report on the body fabric, dated before shipment, records colour fastness to chlorinated water at grade 4-5 and no loss of extension.

Both documents are correct. The fabric passed. The garment failed.

What chlorine actually does, and what it does not

Course 1.2 sets out the chemistry already. Elastane is a polyurethane, which is the stretch fibre in almost every swim fabric. Chlorine attacks it. Ordinary elastane in a swim fabric loses its power in a chlorinated pool within a season, and chlorine-resistant grades exist at roughly two and a half times the price. That is the fibre-level fact, and it is not repeated here.

What is not in that course, and is the whole of this lesson, is this: the tests everybody runs do not measure the failure everybody gets.

Four tests, four grades on a certificate, and not one of them looks at the property the customer complains about. A suit that goes baggy has lost retained power. Retained power is the force the fabric still pulls with at a given stretch after it has been exposed. That is a mechanical measurement, not a colour one.

There is no single agreed method for it. So the specification has to state the protocol itself: the chlorine concentration, the temperature, the total time in the water, the amount the sample is held stretched while it is exposed, and the retained-power figure the fabric has to reach. Two laboratories running "chlorine resistance" without those five parameters will disagree, and both will be right. Course 6.3 makes the general case that the method is half the specification. In swim it is more than half, because for this property there is no method to fall back on.

Sun cream, which has no method at all

Sun cream is the other thing a swim garment meets, and here the position is worse. There is no published international method for it. Laboratories run it as a modified perspiration-type test: the same apparatus and the same procedure, with sun cream put in place of the test solution. So the result depends entirely on which cream the laboratory used, at what loading, for how long.

There are two mechanisms, and they are separate:

• Staining. Mineral filters, mainly titanium dioxide, and some organic filters settle on the surface and yellow it. On a light shade this reads as a permanent brown-yellow mark that no domestic wash removes.
• Degradation. Some organic filters, together with salt, heat and body oil, speed up the loss of elastane power. This is the mechanism the customer feels rather than sees.

So a sun-cream test result is really two results. A specification that asks only for a staining grade has bought half of it.

Where the failure actually was

SW-6208's body fabric was upgraded to a chlorine-resistant construction and certified. The leg elastic, the strap elastic and the shelf-bra elastic were not, and nobody decided that. The tech pack's trim lines read elastic, 8 mm, matching. A width, a colour, and no fibre requirement at all. So Thalna's trim buyer bought the standard article, correctly, against the document in front of him.

The elastic is the first thing to go, and the reasons are physical rather than bad luck. A covered elastane yarn in a narrow elastic exposes far more elastane surface per gram than the same fibre lying flat inside a warp-knit body fabric. And in wear, the leg opening sits at a higher stretch than the body panel does. More exposed surface, more strain, first failure. Thalna's own returns file across four swim programmes shows the same pattern every time. That is evidence rather than proof, but it points the same way as the chemistry.

The two upgrades, priced

The trim upgrade is 6.2% of the cost of the body upgrade. Against a claim of EUR 6,900 it recovers 13.7 times its own cost. And on this garment it protects the component that fails first.

That is the decision this lesson exists for. The body was upgraded because it is expensive and visible on a cost sheet. The trims were not, because they are cheap and invisible on one. The failure went the other way round.

Two other things belong on the same sheet:

• Fabric is a majority line here, unlike the bra. EUR 4.50 of the EUR 8.90 price is body cloth, which is 50.6%. Swim and lingerie sit in the same department and have opposite cost shapes. That is why one cost habit does not serve both.
• The alternative construction. A polyester and PBT fabric gets its stretch from a polyester elastomer rather than from a polyurethane. PBT is a polyester that behaves like a spring. So the fabric is stable in chlorine by construction rather than by treatment, and it dyes as one material. It recovers less strongly, so it suits a beach suit and not a competition garment, and it changes the fit. It is a design decision with a chemistry consequence, taken at line plan, not at costing.

The claim on the ticket decides the fabric

If the swing ticket, the website or the care leaflet says chlorine resistant, that is a claim about the product. Then the resistant construction is not optional, and the whole assembly has to support it, trims included. If it says nothing, a standard construction is a legitimate specification for a beach suit, and the customer has been sold what they were shown.

What is not defensible is a resistant body, standard trims, and a ticket that makes a claim about the garment.

A shade is a returns decision

Here is Aubrette's own return data on this style, one season, both colours made in the same factory to the same specification: Almond returned at 9.1% and Black at 2.6%. The difference is sun-cream staining on a light ground.

That is 6.5 points of return rate bought with a colour card, months before any test was specified. It does not mean light shades should not be made. It means the light shade carries a cost that belongs in the range plan next to it, along with a care instruction on the swing ticket, in the language of the market that buys it, telling the customer to rinse the garment. Course 16.2 costs a range. This is one of the inputs that never reaches the person building it.

Act as a swimwear technologist who has settled claims for lost elasticity. Style facts: [STYLE], [QTY] pieces, colours [LIST], price [PRICE] on FOB terms. Body fabric: [FIBRE BLEND, CONSTRUCTION, WEIGHT, SUPPLIER, PRICE PER METRE, CONSUMPTION]. Every elastic, thread, tape, cup, hook, ring and slider in the garment, with its fibre content if the tech pack states one: [PASTE]. Any claim made on the swing ticket, website or care leaflet: [PASTE THE EXACT WORDS]. Do the following. First, separate the tests that certify COLOUR from any test that certifies RETAINED POWER, and say plainly which of my current package measures the property that actually fails. Second, write a retained-power protocol I can put in a specification, naming every parameter a laboratory would otherwise choose for itself: chlorine concentration, temperature, immersion time, the extension the specimen is held at, the number of cycles, and the retained-power minimum. Third, do the same for sun cream, and state clearly that there is no published international method, so the specification must name the cream, its sun protection factor, the loading, the exposure and the temperature — and treat staining and degradation as two separate results. Fourth, go through my component list and flag every line whose fibre content is not stated, because a line that says only a width and a colour will be bought as the standard article. Fifth, price two upgrades separately: the body fabric and the trims, per piece and on the order, and tell me which component is likely to fail first and why. Sixth, read the claim on the ticket against the specification and tell me whether the assembly as specified supports it. Seventh, list what a light shade costs in returns that a dark one does not. Ask for missing inputs rather than assuming them.