What Dye Migration Is And How To Avoid It
By The Velocity Wear Team
Dye migration is what happens when the dye already inside a polyester garment turns to gas under heat and moves up into the print sitting on top of it. It shows on dark and strongly coloured polyester, and it shows worst in light inks, so a white print on a red poly hoodie gradually goes pink. It is a property of the fabric rather than a printing mistake, but printing choices decide whether it happens to your order.
Why Polyester Behaves This Way
Polyester is coloured with disperse dyes, which do not bond chemically to the fibre. They sit trapped inside the polymer, and given enough heat they sublimate: they pass straight from solid to gas without becoming liquid. Cotton is different. Reactive dyes form a chemical bond with the cellulose and stay where they are put. Once a polyester garment goes past the temperature a standard plastisol cure needs, the disperse dye becomes mobile, and the only place for it to go is up into the ink film.
Why It Often Appears After Delivery
The gassing starts in the dryer, but it does not stop when the garment cools. Migration continues slowly at ordinary temperatures, and warmth accelerates it. Cartons stacked in a warm van, a loft store room or a sunny window finish the job over days or weeks. That is why the sample you approved looked perfect and the photographs your customer sent three weeks later did not. Anyone who tells you the print was fine when it left is usually telling the truth and missing the point.
Which Garments Are Most At Risk
- Dark and saturated polyester, with red, royal, maroon, purple and bottle green the usual offenders.
- Cheaper polyester fleece and sports fabric, where the dyeing was less thoroughly washed off and heat set.
- Poly-cotton blends, which migrate less than pure polyester but still migrate.
- Any design where the print is white, pastel, or carries large light areas.
- Thick ink deposits, which hold heat for longer while they cure.
Lowering The Temperature Is The First Fix
Less heat means less gassing, so low-cure plastisols exist precisely for this problem. They fuse nearer 130 to 140 degrees Celsius rather than 160, which keeps most of the dye where it belongs. The trade-off is a narrower cure window: there is less margin between properly cured and undercured, so the printer has to be more careful, not less. Swapping to a low-cure ink and then running the belt fast to save time gets you a print that does not migrate and does not survive either.
Barriers And Blocker Underbases
The second line of defence is a physical barrier. Low-bleed or blocker white inks are formulated with a dense film designed to trap migrating dye before it reaches the visible colours. The sequence is to print the blocker as an underbase, cure it, then lay the design on top. It costs a screen, a colour station and some hand feel, and it is not absolute, but on dark polyester it makes the difference between a print that holds and one that does not. It is also worth remembering that mid greys, tans and darker inks hide migration well. White shows everything, which is why white is where the complaints come from.
Sometimes The Right Answer Is A Different Method
Sublimation sidesteps migration entirely, because the design becomes part of the polyester fibre with no surface layer at all. The catch is that it only works on polyester and only on light bases, so it suits sports kit and all-over prints and nothing else. DTF sits on polyester well and is a strong choice for detailed work on synthetics, but it still involves a heat press, so it wants low-temperature adhesive powders, a short dwell and, on high-risk colours, a film with blocking properties. DTG is cotton only, so it is not in the conversation. Embroidery avoids heat altogether, which is a large part of why so many polyester softshells and fleeces end up embroidered rather than printed.
Test Before You Commit To The Run
There is one reliable proof and it is not a lab certificate. Print a test on the actual garment, from the actual dye lot, and leave it somewhere warm for several days before you look at it again. If nothing has shifted, the combination works. Ask for that test early, because production runs from artwork approval rather than order placement, and a few days spent proving the garment at the start is far cheaper than reprinting a full run in week four.
“"Polyester dye does not respect the moment you decided the job was finished."”
What This Means For Your Garment Choice
If you have freedom over the garment, use it. A better quality polyester with well fixed dye migrates less. A lighter garment colour removes the risk almost completely. Designing the print in a colour family close to the garment means any migration that does occur is invisible. And if the brief genuinely demands crisp white artwork on a saturated red polyester hoodie, treat that as a technical challenge with a cost attached rather than an ordinary order.