Dye migration most often happens when heat printing onto sublimated polyester. The dye in the garment begins to bleed through the plastisol printed on top. This process can occur when a sublimated garment reaches temperatures of 280 degrees F. To successfully sublimate on polyester, be sure to use a transfer with a dye-blocking agent as well as a low-temperature application. It is also important to note that dye migration won’t happen right away. It could take days to weeks for the dye to bleed through enough to be noticeable.
Source: Jody Mazade, Howard Custom Transfers