These dyes were originally developed for the dyeing of cellulose acetate, and are substantially water insoluble. These dyes are finely grounded in the presence of a dispersing agents and then sold as a paste, or spray-dried and sold as powder. These can also be used for dyeing nylon, cellulose triacetate, polyester and acrylic fibers. In some cases, a dyeing temperature of 130 °C is required, and a pressurized dye bath is used for this purpose. The very fine particle size gives a large surface area that aids dissolution to allow uptake by the fiber. The dyeing rate can be significantly influenced by the choice of dispersing agent used during the grinding.
Polyester generally requires the use of disperse dyes. Other methods of dyes leave the color of polyester almost entirely unchanged. While novices happily charge into dyeing with acid dyes (for wool or nylon) and fiber reactive dyes (for cotton and rayon), often with the most effective results, the immersion dyeing of polyester is a different story.
Disperse dyes work excellent on synthetics, of course - that's what it's for. Only wool, rayon, silk, and cotton refuse to take it. Nylon extensively prefers disperse dye. All others fibers which are synthetic that dyed with disperse dye, so there is some darkness behind the mostly undyed natural fibers.