iDye Poly is for synthetic fibers such as polyester and nylon. It even works on some plastics! The dye comes in a dissolvable packet, so there are never any messy powders to handle: simply drop the packet in a pot of water, bring it to a boil and add your fabric! iDye Poly may also be used for sublimation printing and to dye the poyester threads that are used to sew commercially manufactured garments.