I have always prewashed my fabric for a couple of reasons. Allergies being the biggest. Fabric is made with many chemicals so I try to get that out of my fabric first, Second I want to know if the fabric is going to bleed or not, and I use the Color Catchers you buy in the grocery store in the with the fabric. If the pieces are small, like fat qtrs or charm squares they go in a net lingere bag so I don't loose them in the washer. but to each his own. Some people never wash their fabric. Marge