 In limp binding the covering material is not stiffened by thick boards, although paste-downs, if used, provide some stiffness; some limp bindings are only adhered to the back of the book.Some limp vellum bindings had yapp edges that flop over to protect the textblock.Limp vellum bindings for commonplace books were being produced at least as early as the 14th century and probably earlier, but it was not usually common until the 16th and 17th centuries.