with wide backing, I've found it gets stretched and rolled out of shape. I always prewash mine, and even when it is horrid from the store, it washes and relaxes back into square with the grain. Then I can fold and cut or rip, and it's fine. I also roll my backing on to the top rail and then line it up and pin to the front rail, and roll it from the top to the front to keep a nice tension. A few times I've rolled back and forth between the two to get a better tension on the backing.