I have seen those and they are awesome, im trying to avoid buying any interfacing or anything just working with what I have on hand.
Do you or a friend use dryer sheets? Instead of throwing those away, use them as the foundation for string quilts. Use the ones that are no longer scented or usable for softening. Also, a person can use phone book pages but, of course, that probably needs to be removed. I suppose the paper might "wash out" in time but I would think it best to remove.