Urea is a moisture drawing agent meaning it helps keep the fabric damper for longer.  Fibre reactive dyes stop ‘fixing’ when the fabric becomes dry, so this helps avoid that issue.

Urea prills also have the excellent advantage of being a great dissolving agent.  Some dyes are harder to break down than others, and if you aren’t careful you end up with pockets of dye powder which end up being obvious once you have finished the tie dyeing process.

What do I need in order to tie dye?