Sizing is used to give better 'character' to fabric that is not so great. It is useful in getting patches to behave better in the construction process. Starch or the Best Press product give extra body to difficult areas like bias areas. It is for ease of handling rather than allowing you to incorporate 'limp' fabric. I question using that kind of fabric because the sizing washes away and then you have a patch of fabric that does not behave as the other fabrics do-wear out more more easily. Starch is intended to aid in construction. But, you must use it carefully or the ironing process distorts the bias which is the preceived problem to start with. Bias needs to be handled with care-once it is stretched it cannot be restored to the original shape.