Sublistop
Or also called Block out, means the extra layer that prevents the pigments of the polyester fabric from penetrating through the flex foil or transfer paper after heat from a transfer press. The so-called bleeding. Sublistop is used when sublimated polyester textiles such as sports shirts, football shirts or softshell jackets are printed. Read the explanation here.
Bleeding is a process that occurs when the pigments of a polyester fabric become active again due to the heat. The pigments penetrate the flex foil or transfer paper and this causes a discoloration.
You can prevent this discoloration by using block out foil, also known as sublistop foil. Bleeding is done exclusively on dark colored polyester fabrics, often printed with a lighter colored flex foil.