Machine embroidery water soluble toppers are typically used in very specific situations. Typically called WSS, water soluble toppers are not always needed. They do help in some very specific circumstances, however.
Water Soluble Toppers are used…
1) When the fabric is plush (Minky, faux fur, velvet, velveteen, etc.).
2) When the fabric is loopy (terry cloth).
3) When the fabric is bumpy and you use the topper to help keep the needle from deflecting as much (corduroy).
4) When it is a knit and you don’t want the thread to sink into the knit’s ribs.
5) When the fabric is open and the embroidery foot might catch in the loose weave (burlap or crocheted materials).
6) When you need really clean stitches, such as with small fonts.
7) When you want an easier way to trim small jump stitches, as the topper holds the thread above the fabric for easier cutting with scissor tips.