Colour Fastness in T-Shirts: Tests, Ratings and Buyer Specs

Colour fastness is the least glamorous line on a t-shirt specification and the one that generates the angriest customer emails. It is also a topic wrapped in vague assurances (“excellent fastness”, “premium dyes”) that mean nothing until they are converted into a method, a grade and a tested lot. This guide does that conversion. A shirt that fades unevenly, bleeds onto a white wash load or rubs its colour onto a pale sofa has failed at the one job every buyer assumes is basic: staying the colour it was sold as. The good news is that fastness is measurable, testable and speccable, with international test methods and a simple rating scale that any buyer can put on an order and any serious factory can report against.

We dye and manufacture t-shirts in Bangladesh for brands selling into the USA, UK, Europe, Canada, Australia and the Middle East. This guide explains the main fastness tests in plain terms, what the ratings mean, and the minimum levels worth specifying by garment type.

The Grey Scale: How Fastness Is Rated

Almost every fastness test ends the same way: the tested fabric is compared against a grey scale and given a grade from 1 to 5. Grade 5 means no visible change (or no staining of the adjacent fabric); grade 1 means severe change. Half grades exist, so reports read as 4, 4-5 and so on. Two different judgements are usually scored: the change in the garment’s own colour, and the staining it causes on a standard white multi-fibre fabric washed or rubbed alongside it. A shirt can hold its own colour well and still stain badly, which is why both numbers belong on a report.

Heathers, melanges and neon shades bend the rules in ways worth knowing before they surprise you. A heather’s two fibres take dye differently by design, so its grades are judged against its own standard rather than a flat colour’s. Neons and very bright shades sit near the edge of what cotton dye chemistry holds, and their light and wash grades run lower as a class; speccing them to flat-black standards produces either a failed report or a quietly substituted duller shade. Agree the realistic grades for special shades in writing, with the tested sample kept as the reference.

Buyers do not need laboratory fluency; they need to know which tests matter for their product and what grade to demand. The sections below are the working set for t-shirts, and the standards behind our services and production quality flow reference the same methods.

Wash Fastness: The Headline Test

Wash fastness (tested under ISO 105-C06 or the AATCC 61 method in the US system) simulates repeated laundering in accelerated form: the sample is washed with a standard detergent under controlled temperature and mechanical action, together with a multi-fibre strip that shows what the colour does to other fabrics. For retail t-shirts, a colour-change grade of 4 and a staining grade of 3-4 or better at the care-label temperature is the working retail standard; promotional garments sometimes accept a step lower, and pay for it in reviews.

One clarification that saves arguments later: wash fastness grades the colour’s behaviour in the wash, not the garment’s shape or size stability; shrinkage is tested separately, and a shirt can ace one and fail the other. Specifications should carry both, named as the different tests they are.

The practical variables are the ones buyers control: dark and saturated colours (black, navy, red, deep green) are inherently harder than pastels, some dye classes hold better on cotton than others, and the first washes release loose surface dye even on well-fixed fabric, which is why dark garments carry “wash separately” advice honestly earned. Specifying the test temperature matters too: a shirt rated at 40 degrees that customers boil-wash will be judged by a standard nobody agreed.

Rub Fastness (Crocking): Dry and Wet

Rub fastness (ISO 105-X12) drags a standard white cloth across the fabric under pressure, dry and then wet, and grades the colour transferred. It predicts the real-world failures: dark jeans-style dye on light car seats, a navy tee marking a white bag strap, colour on the inside of a pale jacket. Wet rub grades run lower than dry across almost all fabrics, and deep shades on cotton typically land a grade lower than buyers hope: a wet rub of 2-3 on a saturated indigo-style shade is physics, not negligence, and the honest response is speccing decoration and use accordingly rather than demanding the impossible.

Placement matters in rub testing as much as in wear: the chest under a seatbelt, the side under a bag strap and the underarm are the high-rub zones, and a thoughtful program tests the fabric as the garment will live, not only as a flat swatch on a bench. Prints in those zones get the same wet and dry attention, because print crocking onto skin or straps is judged by customers as a garment fault, not a decoration footnote.

For most tee programs, dry rub 4 and wet rub 3 (or better) is a sound retail line, with pigment-dyed and garment-dyed styles discussed individually because their aesthetic deliberately trades some rub fastness for the washed look the customer is buying.

Light Fastness and Perspiration: The Quiet Tests

Light fastness (ISO 105-B02, rated on a 1 to 8 blue-wool scale) measures fading under UV exposure. It matters most for garments that live outdoors in use or in shop windows in display: workwear, event shirts used across a summer, and retail stock displayed under strong lighting. A grade of 4 on the blue-wool scale is a reasonable floor for general apparel; outdoor-heavy programs spec higher. Perspiration fastness (ISO 105-E04) tests colour under acidic and alkaline sweat simulants, relevant for sportswear and summer basics where the garment sits against skin for hours: collars and underarms are where weak perspiration fastness shows first, as localised fading that looks like a manufacturing fault and is actually a chemistry one.

Prints carry their own fastness behaviour on top of the fabric’s. A well-cured print on a fast fabric still fails if the ink system is wrong for the fibre, and white prints on deep grounds test the eye differently from the lab: the ground colour migrating into the print (or the print’s binder yellowing) reads as a fastness fault to the customer whatever the report calls it. Decoration and fabric should be fastness-tested as the finished combination, which is why the print check sits inside the retail quality sequence rather than in a separate decorative file.

Water and sea-water fastness join the list for swim-adjacent and holiday programs, and chlorinated-water fastness for anything marketed near pools. The pattern to notice is that the test list follows the garment’s life: the right specification is the one built from how the shirt will actually be worn, washed and stored, not the longest list a template can generate.

Why Colours Fail: The Factory View

Most fastness failures trace to four causes. The dye class does not match the fibre or the shade depth demanded of it. Fixation was incomplete, through rushed processing or overloaded dye baths chasing a deep shade. Washing-off after dyeing was shortened, leaving loose dye on the surface to depart in the customer’s first wash instead of the factory’s rinse. Or the fabric itself, a blend or a particular finish, interferes with the dye bond. Each cause has a process answer, which is why fastness is a production discipline before it is a test result: the lab report at the end mostly confirms what the dyehouse did at the start.

Our cotton t-shirt manufacturing programs run fastness testing on production fabric per colour, not on a golden sample from a different lot, because shade-deep production dyeing is where the risk actually lives. Buyers should ask which lot was tested; the answer separates a testing system from a testing ceremony.

Reading a Colour Fastness Test Report Like a Buyer

A fastness report is a short document with a lot packed into it, and four habits make it useful rather than decorative. Check the method named for each test, because a grade without a method is unverifiable. Check the temperature and conditions against your care label, since a pass at 30 degrees says nothing about a 60-degree wash claim. Check which fabric and which colour lot were tested, and when, relative to your production. And check both scores where two exist (change and staining), because the weaker one is the one your customers will meet.

Keep the reports with the order file, and on reorders ask for fresh ones rather than accepting the originals: dye lots, water conditions and even the same recipe at a different depth can move a grade, and the reorder is exactly where a system proves it is a system. Brands that file reports per order also build, almost accidentally, the evidence base that settles disputes and improves specifications season over season.

Setting a Colour Fastness Spec for Your T-Shirt Order

A workable retail t-shirt fastness spec, in plain terms: wash fastness colour change at least 4 and staining at least 3-4 at the labelled wash temperature; dry rub at least 4, wet rub at least 3; light fastness at least 4 for general apparel, higher for outdoor programs; perspiration at least 3-4 for sport and summer lines. Deep and special-effect shades get their variations agreed in writing at order stage, with the test reports from production fabric filed against the order. Promotional programs sometimes relax staining or wet-rub grades for one-wear garments, and that is a legitimate commercial choice when it is made knowingly, documented and priced, rather than discovered.

If you are building a specification for a new program and want it sanity-checked against the colours and fabrics you have in mind, the team via our contact page will walk through it before any order is placed; fastness problems are the cheapest problems in apparel when they are solved on paper.

Frequently Asked Questions