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Colour Fastness in Saltwater

What colour fastness actually measures

Colour fastness describes how well a material keeps its colour when it is exposed to something: light, water, rubbing, sweat, chlorine or seawater. Each exposure has its own test method and its own scale, so a single number without a method attached is meaningless. The two scales you will meet on bag fabric are the grey scale for colour change, rated 1 to 5, and the blue wool reference scale for light fastness, rated 1 to 8.

The grey scale works by comparison. A technician exposes a sample, then places it beside a standard grey pair of chips under controlled light and assigns the rating that matches the observed contrast. Half steps are allowed, so 4-5 is a real result and means the change is slight but detectable by a trained eye. Ratings of 4 and above are generally considered acceptable for outdoor product.

Blue wool works differently: eight dyed wool strips of known light sensitivity are exposed alongside the sample, and the sample is rated by which strip faded to the same degree. A rating of 6 means the sample performed like wool strip 6, which is useful for comparing fabrics but harder to translate into a number of seasons in the sun.

Why saltwater is harsher than freshwater

Freshwater mostly tests whether a dye is water soluble. Seawater adds three things at once: dissolved chloride at about 35 grams per litre, a mildly alkaline pH near 8.1, and, once the water evaporates, crystals that grow inside the weave and between the film and the face fabric. Those crystals are the real problem, because sodium chloride expands as it crystallises and mechanically lifts dye and finish off the fibre surface.

Salt also changes how the surface behaves optically. A dried salt film scatters light, which makes a faded panel look chalkier than the same panel faded in a lake, and it holds moisture against the fabric overnight. That extended damp time matters for hydrolysis in some coatings and for any dye that is only marginally fixed.

Then there is abrasion. On a boat, a salt-crusted bag is dragged across a deck, shoved into a hatch and rubbed against a wet life jacket. Each contact drives crystals into the surface. A fabric that scores well in a static soak can still lose colour quickly in real use, which is why combined cyclic testing is closer to the truth than any single test.

The rating scales and what a point is worth

A single grey scale point is a large difference, not a small one. The scale is roughly logarithmic in perceived contrast: the jump from 4 to 3 is obvious to an untrained eye at arm length, while 4-5 versus 4 is a difference most buyers would never notice side by side. That is why a spec that asks for 4 after 300 hours is far more demanding than one that asks for 3-4.

Commercial practice usually sets acceptance at 4 for colour change and 3-4 for colour transfer to a rubbing cloth. Transfer is judged separately because a fabric can keep its own colour reasonably well and still rub off onto a light-coloured shirt or a boat cushion, which generates complaints even when the bag itself looks fine.

When you compare two fabrics, compare at the same exposure duration. A 4 after 100 hours and a 4 after 500 hours are not the same product, and a report that omits the duration tells you very little. Colour measurement instruments help here: a spectrophotometer returns a delta E value, and a delta E of 1.0 is roughly the threshold of visible difference for a saturated colour.

Pigment in the film versus print on the surface

Waterproof bag fabric fails in two distinct ways, and telling them apart saves a lot of argument. The first path is the body colour: pigment dispersed in the TPU film or dye in the face fabric, which fades gradually and evenly. The second path is any printed layer sitting on top of the film, which can flake, crack or rub away entirely while the body colour underneath is unchanged.

Pigmented film is the more durable route for marine use because the colour runs through the thickness of the layer rather than sitting on it. A 0.5 mm film with pigment through its depth can lose surface gloss and still read as the same colour. A surface print on the same film can lose its sharp edges after 200 hours of salt spray and abrasion.

Prints are not automatically a bad choice. A print protected under a clear film, or a heat transfer that bonds into the surface rather than sitting on it, performs far better than an unprotected screen layer. The question to ask is where the colour sits relative to the wear surface, and the answer determines whether a printed panel survives a season on a deck.

Which colourways survive a marine season

Colour chemistry is not equally forgiving across the spectrum. Dark saturated shades hold longer because there is more pigment per unit area, so a given amount of surface loss removes a smaller share of the visual density. Bright mid-tones, particularly reds, oranges and some blues, use dye systems that are more light sensitive and show fading sooner.

That table describes appearance, not waterproofing. A faded bag still keeps water out, so choosing a brighter colour is a legitimate trade when visibility matters more than looks: a safety orange bag that has gone pale after two seasons is still doing its job on a rescue boat. The point is to enter the trade with open eyes and set an expectation with the buyer.

There is also a heat argument. A black bag on a tropical deck can reach 60 to 65 °C surface temperature in direct sun, against 45 °C for a pale mint bag of the same construction. That extra heat ages the film as well as the colour, so the darkest colourway is not automatically the longest-lived product even though it looks the best for longest.

Chlorine, sunscreen and the other colour killers

Pools are worse than the sea for colour. Free chlorine at 1 to 3 mg per litre is a strong oxidising agent and attacks dye systems directly, and pool water is usually warmer, which speeds every reaction. A bag that lives at a poolside or in an aquapark bag drop will typically fade faster than the same bag used in saltwater.

Sunscreen is the overlooked one. Many formulations contain avobenzone and oxybenzone, and some contain DEET in combination products; these solvents can lift print and plasticise a film surface on contact. Wipe the outside of a bag with fresh water after a day at the beach, and keep sunscreen bottles inside a pouch rather than loose against the fabric.

Other common offenders are insect repellent, fish blood and bait oils, and diesel or petrol fumes in a boat locker. Each of these either solvates the surface or stains it chemically. None of them is covered by a standard colour fastness test, which is why a realistic care note on the product is worth more than another test report.

Test methods you should see on a report

A credible colour fastness report names the standard, the exposure, the duration and the rating scale. Textile colour fastness methods are published by the ISO in the ISO 105 series, which covers light, water, seawater, rubbing and perspiration as separate parts. Corrosion and salt spray practice is documented by ASTM International.

One limitation is worth stating plainly: laboratory light sources are not sunlight. A xenon arc filtered to match daylight is close, but real service adds thermal cycling, salt crystal growth and abrasion that no single standard reproduces. Treat a good laboratory result as necessary rather than sufficient, and ask for cyclic testing when the product will live on the water.

How film chemistry affects colour stability

The polymer carrying the colour matters as much as the colour itself. TPU is generally friendlier to pigment stability than PVC, partly because PVC formulations rely on heat stabilisers and plasticisers that can migrate to the surface and carry dye with them. That migration is also what makes older PVC bags feel tacky and look blotchy.

UV absorber packages change the outcome substantially. A hindered amine light stabiliser plus a UV absorber added to the film can double the time to a visible fade, at a cost of a few percent on the material bill. On a bag with a five-year expected life, that is one of the cheapest durability upgrades available; the mechanisms are set out in more detail in our UV-stabilised fabric guide.

Film thickness interacts with this too. A 0.5 mm film has more pigment depth than a 0.3 mm film of the same formulation, so surface loss has to go further before the colour visibly changes. This is one of several reasons thicker film performs better outdoors, alongside puncture resistance and abrasion life.

Reading a colour fastness report before you commit

Work through a report in a fixed order. Check the identification first: is the sample the same fabric, colour and finish as the production bag, or an early lab dip? Then check the exposure and duration. Then check the rating scale, because a blue wool 6 and a grey scale 4 are not comparable numbers. Only then look at the result itself.

Ask for the delta E numbers alongside the grey scale. A grey scale rating compresses a lot of information into one step, while a spectrophotometer gives you the direction of the change as well as the size. A sample that has gone slightly darker reads differently from one that has gone pale and chalky, even if both land on the same grey scale step.

Finally, ask what the control was tested against. Rubbing results in particular depend on the companion fabric: cotton lawn, wet or dry, and the load applied. A 3-4 result against abrasive wet cotton is a different proposition from 3-4 against a dry smooth cloth, and the report should say which was used.

Specifying colour fastness for a branded range

For a retail or programme range, write the colour requirement into the specification rather than relying on a sample approval. A useful line reads: body colour to reach grey scale 4 minimum after 300 hours cyclic salt spray with UV, and rubbing to reach 3-4 wet. That is a testable requirement, and it gives a production partner something to verify before shipping.

Approved reference samples still matter. Keep a signed retained sample from the approval round, stored in a dark drawer, and compare production against it under the same light. Fading arguments are much easier to settle with a physical reference in hand than with a description in an email thread.

Our production programme has run waterproof bag projects since 2014 in an SGS-verified 4,950 m2 facility, with 7 production lines, 149 machines and 200,000 pieces of monthly output, and colour approval is a standard step in that flow. Minimum order is 500 pieces, sampling takes 6 to 10 working days and bulk runs 35 to 50 days FOB Xiamen.We hold retained colour standards for every programme so reorders match the original shade.

Care habits that slow fading

1. Rinse with fresh water after every saltwater day; focus on the closure fold and the printed panels.
2. Dry in shade with the mouth open; never dry a wet bag on a hot deck or a dashboard.
3. Wipe sunscreen and insect repellent off the outside as soon as you notice it.
4. Store out of direct sun, loosely rolled, away from diesel fumes and bait.
5. Re-rinse pool bags within an hour; chlorine keeps working while the fabric is damp.

Rinsing is the single most effective habit, and it works for a mechanical reason rather than a cosmetic one: you are removing crystals before they grow. A bag rinsed within two hours of a saltwater trip looks noticeably better after a season than the same bag rinsed the following weekend, and the difference widens with every trip.

Store colour-critical bags away from windows. A bag on a shelf in direct sun receives meaningful ultraviolet dose every day of the year, and that dose accumulates even when the bag is not in use. Off-season storage guidance is in rinsing saltwater off dry bags, which also covers hardware corrosion that runs alongside colour loss.

Colour and fabric choices that work together

Colour decisions and fabric decisions are the same decision made twice. A solution-dyed face fabric under a pigmented TPU film gives the best marine result available at a sensible price, because both layers carry their colour in depth rather than on the surface. A piece-dyed face under a clear film is the more fragile combination.

There is a sustainability angle as well. Solution dyeing uses less water and energy than piece dyeing, and a colour that lasts longer means a bag that is replaced less often. See eco-friendly dry bag options and the material comparison in TPU versus PVC, which explains why PVC migration makes colour loss worse over time.

For a range with several colourways, expect different lives. The colour range guide covers how to balance a range so the fragile shades are not the ones carrying the highest volume. The practical rule: put your volume in the stable shades, keep the bright ones as accents, and specify a test level that every shade can actually reach.

Colour fastness checklist

• Ask for the method and the duration, not just the rating.
• Set acceptance at grey scale 4 for colour change and 3-4 for wet rubbing.
• Prefer pigment carried in the film over any colour printed on the surface.
• Choose solution-dyed face fabric where the budget allows.
• Add a UV absorber package to the film for bags that live outdoors.
• Keep a retained approval sample in the dark for comparison at reorder.

Worked example: a resort programme wanted a coral 10L bag for a fleet of 300. Laboratory testing put coral at grey scale 3 after 300 hours of cyclic salt spray, which would have looked tired halfway through a season. Switching the body to a stable navy with a coral printed side panel held the brand look and lifted the body rating to 4, with the print treated as a replaceable accent.

The same logic applies to hardware and trim. A faded bag with bright anodised hardware looks worse than a faded bag with matching hardware, so specify the finish alongside the fabric; see hardware corrosion resistance. Current fabric and colourway options are listed under products, and all marine fabrics are tested to the levels described above.