So, how much will fabric shrink? It depends on what kind of fabric it is, of course. Typically, flannels will shrink between three and six inches per yard when washed! With several high quality flannels (RJR, Moda, and Maywood, for example), however, the flannel may shrink only one or two inches per yard. High quality, quilt shop flat cottons will usually shrink one to three inches. It's not just the yardage length that changes. The prewashed fabric changes size in width and overall shape, too.
From "The Quilter's Ultimate Visual Guide", we can get an excellent description of how fabrics are manufactured. Once you're aware of this process, it can really change your mind if you haven't been a "prewasher" prior to this. Here's an excerpt:
"All 100% cotton fabrics shrink when washed, in part because natural fibers like to remain in a relaxed position. When cotton fabric is produced, the warp and weft threads are pulled taut in the loom, stretching the fibers into an unnatural, straight position. The coatings used by manufacturers further stabilize the fabric, helping threads retain their rigid positions in the cloth even after it's removed from the loom."
The article continues, "When you wash and dry the fabrics at home, most of the restrictive coatings are rinsed away. The movement fibers undergo in both the washer and dryer and their wicking action in water help them relax and allow them to return to a position more like that in which they grew. This relaxation results in what we see as shrinkage."
I like to think of prewashing fabric as allowing the fiber/fabric to "become itself" once again. I also think about people with naturally curly hair (like myself). We shampoo, blow dry, sometimes straighten, and then use hairspray. Compare that process to just shampooing and letting those curls dry naturally! Quite a difference!
In the end, I also like the "feel" of prewashed fabric. I think it's easier to work with prewashed fabric when I'm piecing a quilt, and my longarm machine has a DEFINITE preference for quilting on fabrics that have been prewashed. The fabric has more "body", too. I also like the "look" of prewashed fabrics -- the fibers seem to connect with each other better, giving better color depth.. As for the look of the quilt after it comes off the longarm machine? Many times, you can hold up a quilt to the light and see bits of light coming through thousands of needle holes in fabric that has not been prewashed because the sizing holds the fibers so taut that they can't close in around the tiny holes made by the needle!
I'm often asked about my prewashing techniques. Here's what works for me -- I put some warm water and a small amount of laundry detergent (maybe a teaspoon or two) in the laundry tub. I put the fabrics into the tub (lights and darks in separate batches) and let them them soak for ten minutes or so. I drain the tub, rinse the fabrics, let them drip dry in the laundry tub for a few minutes, and then I hang them over an old-fashioned wooden drying rack (I bought mine at Target). By avoiding the washing machine and electric dryer, I am able to drastically minimize raveling and also minimize the ironing time that follows drying. I even prefer lightly ironing the fabrics when they are not quite completely dry! The process yields fabrics that are wonderfully ready for piecing and quilting!
In the end, I admitted to Carole that I often dislike prewashing fabrics because I just want to get started with the beautiful new fabric. I have to stop and tell myself that the few hours it takes is a small inconvenience when thinking about about the entire project.