What is water-soluble topping and how should I use it?

Water soluble is a topping that dissolves in cold water.

It would be used on textiles and garments that are fluffy or textures, such as fleece or towels. 

The water soluble topping is used on top of your garment, so that the material does not appear through the embroidery, and then simply disolved in cold water to reveal perfect stitch quality.