I especially use Retayne on Batiks ... Batiks is what got me started using Retayne.
Synthropol is for use once a project is completed, and fabrics have not been treated with Retayne. Syntropol will not keep the fabrics from running/bleeding it justs suspends the released dye so it does not discolor the reamaining textiles. Note Syntropol is to be used in warm water, and the company recommneds once Synthropol has been used all subsiquent washes of treated must be washed in warm as well.
Retayne works to lock in the dyes not just work with excess that is released. Once Fabric has been treated with Retayne , wash in cold water.