From Tie-dye Wiki
There are several types of fiber reactive dyes. Procion MX Fiber Reactive dyes are most commonly used wth tie-dye. See Procion Dye Concentrations for guidelines in mixing the dyes for direct application.
The advantages of fiber reactive dyes include ease of use, brilliant colors, relatively low toxicity, and good washfastness. Unlike all-purpose dyes, the cool water fiber reactive dyes do not need to be boiled or steam-set, and they last far longer on frequently laundered clothing.
The one essential auxiliary chemical for dyeing with fiber reactive dyes is soda ash, or sodium carbonate. Other auxiliaries, such as urea, sodium alginate, and salt, are optional, depending on the methods being used and the desired results.
Procion MX dyes can be used to dye cotton, rayon, linen, hemp, tencel, and other cellulose fibers, as well as silk. To dye wool or nylon, it is necessary to substitute an acid, such as vinegar, for the soda ash normally used in tie-dye, and additionally to provide a source of heat.