When I have to piece my backings, I use Elmer's Glue to tack down the seam pressing it down with the iron. This way I know it won't get fluffed up while advancing the quilt sandwich during quilting. I wash all my quilts afterwards before giving to the recipent. I used one of my quilts just the other day to keep warm and found for some reason I hadn't washed it yet but didn't notice any stiffness from the glue as I also use it to attach the binding during the stitching process.