I never used to prewash. However, I prewashed all the fabric used in my last quilt (cotton). And I washed the batting (Cotton with scrim). All items were washed in warm water and dried in a dryer on medium setting,.It was long arm quilted with poly thread. The finished quilt measured 65 x 117 inches. I washed the finished quilt and it shrunk, 5 inches in width and 7 inches in length. I thought prewashing would have eliminated shrinkage of the finished item. Has anyone else had this happen?