I pre-wash as you never know what kind of dust/dirt it has collected especially for those with asthma or allergies but most of all colour fastness. My very first experience of quilting - a 12 part kit Baltimore BOM by a well known company where they furnished the fabric. I quick-washed but didn't double rinse. The quilt was finished except for the binding and when being spritzed with water to remove quilting lines the colours ran! Some so badly right throught the batting and onto the backing. Bless the dear people on this board who recommended synthrapol which removed the mess and saved the day. So pre-wash and double rinse.