Admittedly I do not pre-wash all my fabrics but I do some of them. Normally by the feel of the fabric in the store. I compare bolt to bolt. If one feels different, even slightly, I know that it could mean trouble. Even though fabrics are grouped together does not mean they came from the same mill or the same batch. A long time ago I purchased such a fabric and I still run into it from time to time and it is still stiffer than most of the other fabrics in my stash.