If you are going to use single fold, then on the bias would be stronger than on the straight of grain, but then I don't think that would be a very economic option, fabric wise. For a half inch single fold binding, you are going to need a minimum of 1.5 inch strips ( and that would be tight, because of the depth of the batting). For a double fold, minimum 2.5 inch strips - do you really need to save an inch each time?