Knitted Bag Colour Fastness by Yarn: A Comparison Matrix for Rubbing, Washing, Light and Perspiration

Four Colour Risks a Knitted Bag Actually Faces

Four exposures account for almost every colour complaint on a knit bag: rubbing against clothing, laundering, sunlight, and perspiration or hand oils.

Rubbing is the one customers notice first, because it transfers colour onto a light shirt or a car seat. Laundering is the one that generates returns, because a bag that bleeds in the wash also stains what is washed with it. Light is the quiet one: it does not produce a complaint for months, by which time the style has already been reordered.

Each exposure has its own method and its own pass grade, and they do not correlate perfectly. A yarn can grade 4 to 5 on dry rubbing and only 3 on wet rubbing, which is why the specification should list all four rather than one representative figure.

Structure changes the picture as much as fibre does. A plain jersey presents the loop crown to whatever it rubs against, while a rib or an interlock buries more of the yarn below the surface. Two bags made from the same dyed yarn can therefore grade differently on the same test, which is why the specification should record the stitch structure alongside the yarn.

Matrix 1: Rubbing Fastness by Yarn

Rubbing fastness is graded on the grey scale from 1 to 5 to AATCC TM8 or ISO 105-X12, and the wet reading is nearly always the lower of the two.

The pattern worth remembering is that dope-dyed yarn sits at the top of the table because the pigment is inside the filament rather than on it. Where a programme has a rubbing complaint that will not go away, switching the dye route usually solves it faster than changing the fibre.

Grades are assessed against the grey scale in half steps, so a reading of 4 to 5 sits between those two full grades. Recording the half step matters, because a programme that only writes down 4 loses information that later distinguishes an acceptable lot from a failing one.

Matrix 2: Washing Fastness by Yarn

Washing fastness is graded for both colour change and staining of adjacent fabric, normally to AATCC TM61 test 2A at 40 °C.

Two grades are reported because they describe different failures. Colour change tells a buyer whether the bag goes dull or shifts hue; staining tells a buyer whether the bag ruins what it touches. Retail programmes usually set the pass line at grade 4 for change and grade 3 to 4 for staining.

Washing results also depend on the cycle count and temperature written into the test. A five-cycle test at 40 °C is the common retail request; a single cycle at 30 °C will grade higher on the same fabric and is not comparable. Always record both numbers on the specification so two quotes describe the same exposure.

Matrix 3: Light Fastness by Yarn

Light fastness is graded to ISO 105-B02 on a 1 to 8 blue wool scale, and it is the test where fibre choice matters most.

Pale shades are the weak point across every fibre, because there is less colorant present to lose before the shift becomes visible. Where a programme needs a pale shade and outdoor exposure, dope-dyed polyester is usually the only specification that clears both requirements.

Light fastness is also the test most affected by shade depth. A deep navy can grade 6 where a pale stone of the same dye formulation grades 4, simply because there is more colorant present. Where a range includes both, set the pass grade per shade rather than once for the whole style.

Why Dye Class Drives Every Result

Fastness is decided by the dye class and how it is fixed, not by the fibre alone: disperse dye in polyester behaves differently from acid dye in nylon, and the fixing step matters as much as the dye.

Polyester dye class

Disperse, applied near 130 °C

Polyamide dye class

Acid, applied near 98 °C

Rubbing method

AATCC TM8, or ISO 105-X12

Washing method

AATCC TM61, test 2A at 40 °C

Light method

ISO 105-B02, blue wool scale

Perspiration method

AATCC TM15

Grey scale for change

1 to 5, grade 4 typical pass

Colour tolerance

Delta E 1.0 virgin, 1.2 recycled

Post-dye treatment

Reduction clearing for polyester

Specimen conditioning

Standard atmosphere before assessment

Reduction clearing is the step most often skipped under time pressure, and it is the one that shows up in wet rubbing results. It removes unfixed disperse dye sitting on the fibre surface; without it, the surface dye transfers to whatever the bag rubs against, particularly when damp.

Fixing matters as much as selection. An acid dye applied to nylon at 98 °C without a fixing after-treatment will wet crock badly even though the shade looks right on the bench. Where a programme keeps failing wet rubbing, the after-treatment is the first place to look, not the fibre.

Dope Dyed Against Piece Dyed: The Fastness Gap

Dope-dyed yarn grades about one to one and a half points higher on light fastness than piece-dyed yarn of the same fibre, because the pigment is locked inside the filament during extrusion.

The trade is timing against performance. A programme with a stable core shade repeating every season should dope-dye it; a programme testing a new colour should piece-dye until the shade proves itself, then convert.

Dope dyeing also changes the commercial shape of a programme. Because pigment is added at the spinner, the colour must be committed before knitting starts, usually against a minimum of about 300 kg per shade. That suits a core colour with a known repeat and works against a shade that is still being tested.

Where Blends Behave Differently

A blend grades like its weakest component on each test, which is why a 50/50 recycled cotton and rPET shell needs both components assessed separately. Where a programme needs one pass figure for a blended shell, take the lower of the two component grades rather than an average, and state that convention on the purchase order.

• Rubbing — the cotton component governs, so expect grade 3 to 4 wet unless the surface is cleaned up.
• Washing — check staining on both cotton and polyester adjacent fabric, since the two fibres pick up different dyes.
• Light — test the dyed cotton component separately, as heather effects can mask a marginal result.
• Perspiration — nylon and cotton blends can shift under acidic conditions, so test at both pH values.
• Chlorinated water — relevant for pool and beach programmes, and rarely covered unless specifically requested.

The general caution is that a blend is not an average. The composite result is set by whichever component fails first on each exposure, and a specification that quotes a single figure for a blended shell hides that.

For a blended shell, the practical approach is to test each component separately and then test the composite. The lower of the two component grades is what the composite will tend towards, and knowing which fibre is holding the result back tells a buyer where to spend money.

Reading a Lab Report Correctly

A usable lab report names the method, the test conditions, the specimen description and the grade for both colour change and staining — anything less cannot be compared against a specification.

Three checks catch most problems. Confirm the method matches the one named on the tech pack, because ISO and AATCC methods differ in ways that move the grade. Confirm the specimen is the finished fabric rather than the yarn, since structure affects the result. And confirm the report states both change and staining, because a good change grade sometimes hides a poor staining grade.

It is also worth asking which side of the fabric was tested. On a knit bag body, the face that rubs against clothing is usually the technical face, and testing the reverse gives a result the customer will not recognise.

Conditioning is not a formality. A knit specimen that has dried out will read differently from one held at standard atmosphere, and the difference is largest on the fibres that absorb the most moisture. Two competent labs can disagree by half a grade purely because one conditioned the specimens and the other did not.

What to Write Into the Specification

Six lines on the tech pack settle colour fastness: method, dry grade, wet grade, wash grade, light grade and colour tolerance.

Name the method for each — AATCC TM8 for rubbing, AATCC TM61 2A for washing, ISO 105-B02 for light — and set the pass grade beside it. Add the colour tolerance against the approved swatch, Delta E 1.0 for virgin and 1.2 for recycled, and state that specimens are conditioned before assessment. Then inspection follows AQL 2.5 to ISO 2859-1, which makes all six enforceable at goods-in.

The last piece is the retained reference. A swatch from the approved lot, stored away from light, is what allows next season's lot to be judged against something real rather than against a memory of the colour. Programmes that skip this step spend the following season arguing about whether the shade has drifted.

A specification written this way also shortens disputes. When a lot is questioned, the question is no longer whether the colour looks right, but whether it met a grade that was agreed in writing before the yarn was ordered. That is a much faster conversation.

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