After dyeing or printing, the surface of textiles has some unfixed or hydrolyzed dyes (commonly known as floating color). And if we don't let the unfixed dye remove, it will not only affect the color fastness of the product, but also influence the brightness of the color.
To eliminate these floating on the surface of the fabric, washing with water alone is useless. You must use soaping agent, so the fabric can reach its perfect rubbing fastness, wash fastness and vividness. During soaping or reduction cleaning (cleaning after PET disperse dye reduction), generally we require to add surfactant to increase washing efficiency.