Dyeing FAQ: What is urea for? Is it necessary?
Urea is used in tie dyeing and other forms of direct application of dyes. It is usually not used in vat dyeing or low water immersion dyeing. Urea has two purposes: it can make it possible to dissolve more dye in a given volume, for the strongest of colors, and it serves as a humectant, or water-attractor, to help keep fabric damp long enough for the reaction to occur. You can do without urea if your dye solutions are strong enough for your needs without it, and you keep your fabric damp in some other way, such as by covering with plastic. Too much urea can actually make it harder to dissolve some dyes, according to Craig Turner of Standard Dyes, who says that, if your dye (especially fuchsia, Procion red MX-8B) is not dissolving well, you may need to reduce the amount of urea you are using.
