Urea

Urea, when used for tie dye, is an optional chemical that helps dyes stay wet longer and penetrate fabric. It's use when mixing liquid dye to get vibrant color.

Some people like to use this when they are mixing up big batches of chemical water. It's something liquid dyers prep ahead of adding dye to the water. It can contain thickening agents, urea or salts to make the dye behave for their specific technique.

I don't see ice dyers using urea in their process very often, and I have never used it with ice dye.

I need to do more experiements to see where the most value comes with using urea.