Poly Blocker Formula
A dye-migration blocker printed below the white underbase, the layer that keeps a red polo from turning pink six weeks after the press.
Short version, straight from the floor.
Poly blocker is a specialized underbase ink layer engineered to stop dye migration on polyester and high-poly-blend fabrics. Dye migration is what happens when the disperse dyes used to color polyester sublime under press heat, pass through the ink layer, and re-crystallize on the surface of the transfer. Two weeks or six weeks later, the customer opens their drawer and finds their white logo has turned pink, their yellow gone orange, their red faded to salmon.
Trusting the shirt tag over the actual fabric. Some blanks tagged '50/50' are actually 65/35 poly-heavy. Some 'triblend' garments have enough polyester to migrate. If you can pinch the fabric and it feels slick, treat it as poly and add blocker.
Pressing poly blocker at cotton temperatures. Blocker cures at 230 F, transfer presses at 275 to 285 F on performance fabric. If your operator sets the press to 320 F out of habit, the disperse dye is going to sublime through the blocker anyway. The blocker is a barrier, not a magic shield.
Assuming blocker fixes an over-heated garment. If the shirt is scorched, migrated, or shiny from too much press heat, blocker is not the fix. Blocker is a preventive layer. Reprint on a fresh shirt at the correct temperature.
Skipping blocker because 'the customer will not see it for a while.'. They will see it in the mirror after wash three. And the complaint email that follows is more expensive than the ink pass. Print the blocker.
A production-floor definition, not a spec-sheet lift.
Poly blocker is a specialized underbase ink layer engineered to stop dye migration on polyester and high-poly-blend fabrics. Dye migration is what happens when the disperse dyes used to color polyester sublime under press heat, pass through the ink layer, and re-crystallize on the surface of the transfer. Two weeks or six weeks later, the customer opens their drawer and finds their white logo has turned pink, their yellow gone orange, their red faded to salmon.
The blocker layer contains pigment binders and heat-stable resin that trap migrating dye molecules before they reach the visible color layer. It is printed first, then cured, then the standard white underbase goes on top, then CMYK. The blocker is invisible in the finished transfer, but it is the layer that decides whether the shirt is still the right color at wash 30.
Not every DTF vendor prints poly blocker. Some do not have the ink and cure profile to run it. Some charge extra as an upgrade because the ink is more expensive per pass. Golden DTF prints poly blocker at no upcharge on any transfer that gets flagged as high-poly at order intake. Any Gildan performance style, any Sport-Tek, any Nike Dri-FIT, any bright-color polyester substrate.
It matters most on light-color art over red, navy, kelly, black, or maroon polyester. Those disperse dyes are the most active under heat. It matters less on dark-color art over light polyester, where any minor migration is hidden by the ink itself. If you cannot tell whether your job needs blocker, send us the garment and the file, we will call it.
Every field you need before the press cycle starts.
The numbers below come from our own production floor, not a supplier tech sheet. If a field says 305 F, it is because we press at 305 F and it works. If a field says "avoid on tri-blend," it is because we ruined a run and stopped doing it.
Physical
- Ink type
- Pigment-loaded polymer barrier resin, water-based
- Deposit range
- 5 to 12 grams per square meter, always below the white underbase
- Cure temp
- 230 F cure lamp before underbase pass
- Layer order
- Film → poly blocker → white underbase → CMYK → adhesive powder
When required
- Always required
- Light-color art on red, kelly, navy, black, or maroon polyester
- Recommended
- Any garment above 50% polyester in a saturated color
- Optional
- 50/50 cotton-poly blends in soft or heather colors
- Not required
- 100% cotton, tri-blend, or dark-color art over any substrate
Behavior on garment
- Migration protection
- Blocks 90%+ of disperse-dye migration up to 60 washes at standard care
- Hand impact
- Adds negligible hand; the layer is thin and flexible
- Press recipe adjustment
- Drop press temp 10-15 F from cotton default (275-285 F on performance)
- Peel
- Runs on both hot-peel and cold-peel; cold-peel recommended on stretch performance knits
- Wash durability
- 60-plus washes with intact color
Cost & workflow
- Cost per unit at volume
- Included on flagged orders; no upcharge for verified high-poly jobs
- Line speed impact
- Adds one additional print pass; roughly 8 to 10 percent slower per transfer
- Common failure mode
- Not printed because the vendor did not identify the fabric as poly. Migration shows up 4 to 8 weeks later.
What this is designed to run next to.
Every pairing below is one we set on the press ourselves. If a substrate or transfer type is not here, it is either wrong for this material or we have not proven it enough to publish.
Best-with garments
Best-with films
Where this is the wrong tool, and what to reach for instead.
The garment is 100% cotton.
Cotton dyes are reactive, not disperse. They do not migrate under press heat. Adding poly blocker to a cotton job costs money and adds hand for zero benefit. Skip it.
You want to save cost on low-consequence merch.
If you are pressing 500 giveaway tees where nobody is going to notice a slight color shift six weeks out, skipping blocker on a light-color-on-poly job is a defensible cost-cut. Just do not do it on retail merch or roster jerseys where the customer will notice.
The design is a dark color on a light polyester shirt.
Migration goes from the fabric into the ink. If the ink is already dark, minor migration is invisible. Save the blocker pass for the jobs where a color shift would be noticeable.
The failures we watch shops repeat every week.
Trusting the shirt tag over the actual fabric.
Some blanks tagged '50/50' are actually 65/35 poly-heavy. Some 'triblend' garments have enough polyester to migrate. If you can pinch the fabric and it feels slick, treat it as poly and add blocker.
Pressing poly blocker at cotton temperatures.
Blocker cures at 230 F, transfer presses at 275 to 285 F on performance fabric. If your operator sets the press to 320 F out of habit, the disperse dye is going to sublime through the blocker anyway. The blocker is a barrier, not a magic shield.
Assuming blocker fixes an over-heated garment.
If the shirt is scorched, migrated, or shiny from too much press heat, blocker is not the fix. Blocker is a preventive layer. Reprint on a fresh shirt at the correct temperature.
Skipping blocker because 'the customer will not see it for a while.'
They will see it in the mirror after wash three. And the complaint email that follows is more expensive than the ink pass. Print the blocker.
Materials this is often confused with.
Flag your job as high-poly and we handle the rest.
Send the garment brand and style at intake. If it is polyester or a poly-heavy blend, we lay the blocker automatically. No upcharge, no supplier-lottery guessing about what your vendor did or did not print.