I used to pre-wash everything. Now I don't. I use these fabrics together and have never had a problem. However, I do use the color catchers in the wash after I finish a quilt. I have never noticed different amounts of shrinkage. Someone, above mentioned shrinkage of one-half inch on a five inch square. That translates to 3.5 inches in a yard of fabric or 10 percent. Can't imagine that!