I use either used dryer sheets or fabric that is too thin to use for the face as a base for both string and crumb quilts. Using a fabric base stabilizes the scraps that are being sewed together. Sometimes I use very small pieces for crumb quilts. For the string quilts, I use whatever strings that I have. They may be wider on one end than the other. This means that one side of the strip is on the bias. The foundation stabilizes it. I just use a strip cut in the opposite direction for the next string.This method does not result in as pretty quilt as one where uniform width strips that match with the previous block, but it uses up more scraps and makes a perfectly good utility quilt. It is easy, mindless, relaxing sewing, and some people especially like the effect.