I've been quilting for 32 yrs and at the beginning, I used to prewash everything. I don't anymore except for maybe if I am using a really dense color like red. That is the only fabric I have used that has run. The fabric quality is much better than it used to be with minimal shrinkage. Why do all that work, ironing a large piece of fabric is such a pain. When washing a completed quilt, I just love the crinkled look.