Anti-dye-migration chemistry.

A barrier laid between fabric and image, so that when heat sets a polyester garment's own dye moving there is something in its way. In screen printing that is a blocker base rather than a white one: FN-INK sells its Barrier Black as a carbon blocker base and argues that a white base makes the weaker wall. How it is printed decides whether it works at all. The same page describes the failure that follows a bad choke: if the top white overlaps the blocker and touches the fabric, colour creeps up that edge and halos into the print, days after the boxes went out. On the digital side, Kornit lists Karbon Shield with a jetted blocker it calls DigiBlocker and claims it removes dye migration in both direct-to-polyester and direct-to-film work. Chemistry is one lever and heat is the other, so a blocker does not license a dryer running hotter than the blank can take, which is what low-cure ink exists for.