Can you explain what I need to make custom coasters and how it is done?
Blank coasters come in a range of materials including paper-cardboard, cork, hardboard, sublimation fabric, and wood. If you purchase a blank coaster from a sublimation supplier, then these all can be decorated with a sublimation transfer.
Cork also can be decorated using a clear printer-cutter material, or it could be printed with a digital direct-to-substrate printer. You also could decorate paper-cardboard coasters with a digital direct-to-substrate printer.
In theory, you could put a printer-cutter transfer on any type of coaster, but I do not recommend this. The vinyl is not absorbent, and it can look less professional than other decorating methods.