Disperse dye.

Disperse dye is the class of non-ionic, barely water-soluble dyes made for hydrophobic synthetic fibers such as polyester, the polyamides including nylon, and cellulose acetate, and sublimation transfer requires it. Under heat the dye migrates into the amorphous regions of the polymer, above the fiber's glass transition, and is held there by van der Waals and hydrophobic forces rather than by a chemical bond, which is why the color ends up inside the fiber instead of on top of it. Cotton offers none of that: cellulose is hydrophilic, it does not soften at press temperature the way polyester does, and a non-ionic dye has almost no affinity for it, so a sublimated image on cotton sits on the surface and washes out fast. That is why the poly count belongs on the order form and not in the operator's head, because the complaint comes back weeks later from the customer's laundry, long after your QC signed the box.