A navy bag that leaves a blue mark on a light shirt becomes a return, a review that mentions dye, and sometimes a chargeback. None of it shows on the approval sample. It shows up after a humid container, three weeks in a sunny window, or the first wash. Fastness is the least glamorous line in a tech pack and one of the few that decides whether a program gets a second season.
One bag, five dye recipes
Color is rarely one decision. The shell is usually polyester or nylon dyed with disperse dyes; the lining may be a lighter cloth in another fiber; webbing is a separately dyed tape; thread comes from another mill; printed panels and PU trim sit on top. Five components can read as the same navy under a light booth and age in five directions.
So fastness has to be specified per component: a shell that grades well says nothing about the webbing running across a shoulder. This sits alongside the shade approval process in bag color matching and lab dips and the choices in the lining fabric guide.
The four tests that map to real complaints
Rub, or crocking. ISO 105-X12 and AATCC 8 both use a crockmeter: a weighted finger rubs a white cotton cloth across the specimen, dry and wet, then the staining is graded against the grey scale in ISO 105-A03. This predicts dye onto a shirt collar, a car seat or a gym bench.
Light. ISO 105-B02 and AATCC 16 expose fabric to xenon arc light beside blue wool references. Anything living in a window, on a beach or strapped to a bike needs it. A laptop sleeve that stays inside another bag mostly does not.
Wash and water. ISO 105-C06 or AATCC 61 covers laundering, ISO 105-E01 water spotting. Worth specifying for a washable tote or gym bag; largely a formality for a structured travel piece.
Perspiration. ISO 105-E04 uses acid and alkaline sweat solutions. It matters for handle wraps and back panels pressed against skin for an hour in heat.
Reading a grey scale grade like a buyer
Grades run 1 to 5. A 5 means no visible staining, 4 slight, 3 noticeable at conversational distance, below 3 a complaint in waiting. Many programs land on dry rub 4 and wet rub 3–4 for dark shades, with light fastness 4 outdoors. Treat those as starting points; what matters is writing the number down before production.
Two things trip buyers up. Dark shades are genuinely harder — deep reds, royal blues and true blacks carry more unfixed dye than mid tones, so demanding wet rub 4-5 on a red can mean a different recipe with a higher cost and a larger minimum. And wet results usually run a half to a full grade below dry, because water carries surface dye. That is normal, not a defect, which is why the two are graded separately.
Why dark shades bleed, and what mills do
Most failures are unfixed dye on the fiber surface rather than inside it. Mills strip it by reduction clearing polyester, by thorough soaping of reactively dyed cotton canvas, and by fixing agents where the fiber allows. Coatings complicate matters: a PU or TPU film over a marginally fast fabric can hold loose dye near the surface and make rub worse, not better. Worth raising while the material line is still open — see the fabric denier and coating guide.
Solution-dyed yarn is the structural fix. Pigment enters the polymer before extrusion, so light fastness is excellent and color runs through the yarn instead of sitting on it. The trade-offs are a narrower shade range and usually a higher minimum, which puts it out of reach for a first small run.
Making the line enforceable
“Color fastness: good” cannot be enforced. A usable line names the test method, the substrate, the minimum grade and when it is verified. Decide whether mill test reports per dye lot are enough or whether pre-production samples go to a third-party lab such as SGS, Intertek, Bureau Veritas or TÜV, and put that in the purchase order rather than an email.
Test the finished panel as well as the roll: printing, heat transfer and welding all change the surface, so a sublimated panel needs its own rub test after printing — the sequencing point made in custom bag logo methods. Keep a retained swatch from the approved lot too, since repeat orders drift and drift is judged against a physical reference.
The same enforceable-spec habit applies to metal hardware: a grommet or eyelet whose plating fades in testing is the same class of failure as a bleeding dye.
Frequently asked questions
Is grey scale grade 4 good enough for retail?
For dry rub, 4 is a common retail target. Programs selling light product beside dark bags often push wet rub to 4 as well and accept a better dye recipe.
Why is my wet rub result lower than dry?
Water mobilises dye sitting on the fiber surface. A half to full grade difference is typical on deep shades, which is why the two are graded separately.
Do I need light fastness testing if I only sell online?
Only if the product is used outdoors or displayed in daylight. It adds cost and lead time, so match it to the actual use case.
Who pays for third-party fastness testing?
No fixed rule. A common arrangement is mill reports at the mill’s cost for each dye lot, with third-party verification on pre-production samples paid by the buyer. Agree it in the purchase order.
Related reading
For the wider material decision that comes before testing, see how to choose bag material. Record the pass mark inside the same AQL inspection level used for the rest of the order.