There is no difference in terms of color or dye performance. The liquid dye is already dissolved in water and more concentrated than the powder dye. So you only need to use half as much when using the liquid dye. Also, since the liquid dye is pre-mixed, this eliminates the need to dissolve the dye in hot water as you need to do with the powder dye before adding it to the dyebath. As a guideline, one bottle of liquid dye is equivalent to two boxes of powder dye.