I remember spending lots of time helping my mom stretch fabric, and now I try to do it when the grain doesn't line up. I was told by someone that if the fabric has polyester or other synthetics in it, that it won't work. I have also notice that more and more fabric, including 100 % cotton, is cut way off grain. If you straighten it,you can lose a lot, and if you only bought a small amount and need most of it, that can cause a major problem.