I am a prewash every fabric person. I want the sizing removed for applique and the grain of the fabric to relax and straighten out. This trick makes washing those large pieces easy and you don’t get wadded up wrinkles.
Open up the fabric all the way so it is a single layer. Accordion fold along one selvage edge, about 15-18 inches wide. Using rust free quilting pins, pin through all layers, every 2 inches. DON’T pin the other selvage. Wash, either by machine or by hand.
When it comes from the washer, it will look a mess. DON’T try to straighten it out. Just toss it in the dryer and dry.
When it is dried it will look better, but not much. Don’t panic. Rummage around in the fabric until you find the selvage edge where the pins are. Grip that in both hands and start shaking. After a dozen or so good brisk shakes, most of the folds will have returned to the right spot with no twisted up wrinkles.
Here we have, washed and shaken out fabric. No wrinkles and very few frayed threads on the cut edge.