Polyester is dyed with disperse dyes that can move out of the fibre when heated. In a printed garment, those dye molecules can migrate up into the print layer, which is why a white or light print on red, navy or black polyester can turn pink, grey or tinted. It often shows up after a delay, because warm storage, stacking pressure and long shipping times speed it up. Cotton-rich fabrics are less prone, but polyester blends can show it.

Why it appears after inspection

The print can look fine when it leaves the printer and change in cartons over days or weeks. Heat, pressure and time all increase migration, so tees stored in hot containers or warehouses are most at risk. A final inspection on the day of packing will not catch it, which is why testing before production matters.

Ink and process choices

Ask the decorator whether the ink system is made for polyester and has a migration-blocking or low-bleed base layer. A blocker underbase, a correct print thickness and avoiding too-high curing temperature or too-long dwell time all help. Plastisol and some other inks differ; ask for the decorator’s data on your fabric type and dye.

Fabric and dye

Some disperse dyes are more prone to migration than others, and deep reds and darks use more dye. Ask the mill or dye house whether the dye selection takes migration into account, and whether the fabric has been washed or reduction-cleaned after dyeing, which removes loose dye from the fibre surface.

Test before bulk

Print a strike-off on the actual bulk fabric and store it under warmth and pressure for a set time in a stack, then compare it with a sample kept cool. Ask your lab or decorator for its migration method. ISO 105-P01 tests colour fastness to dry heat excluding pressing, with colour change and staining assessed, and may help as a supporting test; check with your lab which method fits. Also check colour fastness to washing with ISO 105-C06 and a wash with ISO 6330.

What to write in the order

Specify ink system and underbase, maximum cure temperature, and a migration test on bulk fabric as a condition of release. Keep an approved aged sample as the reference.