Sublimation is the process from a solid state to a gas state bypassing the liquid state. Sublimation systems work the same way. Your inkjet printer, will print onto a specially coated sublimation paper with special sublimation inks. When it dries onto the paper, the ink is in solid form.
Once you apply heat and pressure on the solid inks, they quickly become gas bypassing the liquid state. Because of the pressure and heat, the gas slowly and accurately moves from the specially coated paper to the polyester coated substrate. Once heat is taken away and the ink is allowed to cool, the gas is then trapped in the polyester coating. Thus, the image is permanently trapped in the polyester coating.
Without the polyester coating, the inks cannot be trapped. Only some synthetic materials will allow the inks to go into it and to trap the inks inside. Because the inks are translucent (part transparent, and part opaque), sublimation will not work on dark colored substrates simply because the dark background will show through and contaminate the image. In a worse case scenario, the dark background may make the image completely not visible.
In addition, not all inkjet printers can use sublimation inks. The reason for this is because some inkjet printers use heat to print. Because heat is used in the sublimation process, heat cannot be used during printing on the printer, as it will allow some of the inks to evaporate and color consistency cannot be achieved. Thus there are only a hand full of printers out there that can use sublimation inks.
Sublimation also requires a flat or consistent surface. the reason for this is because the heat needs to be applied evenly in all areas at the same time for the image to print onto the hard substrate. If heat is not applied evenly, the image quality will not be consistent.