Magic Sizing doesn't scorch as easily as starch so I use it on light fabrics. It doesn't get as stiff as starch either so if you're just wanting a little body, use sizing. If you want it stiff, use starch. Starch is also cheaper and if you buy the concentrated stuff, you can mix it however you want it. I haven't seen that option in sizing. Seems to be a "one can fits all" thing.