I used to pre-wash my fabric, iron it and store it. But I found that I liked working with unwashed fabric better and now I do not pre-wash. I do mix washed and unwashed because I have them. After I finish a quilt I wash with color catchers-just in case. I, obviously, can no longer see a difference in the fabrics used. I use good quality fabric and have never had problems. I sew for a charity group that provides materials (cheap as possible because of budget constraints). The difference is astounding. There are a lot of considerations to buying and using fabric. You do get what you pay for.