Bookbinding structures consist basically on sewn or adhered components. The type of attachment of each part to the rest defines the mechanism a book will function and be handled.
Conservators are compelled to preserve the main supports unaltered and yet precisely because structural parts allow the functioning of the object it is often accepted that when they are damaged they are better replaced rather than solely preserved. However, restoring the original structure is not always enough, specifically for disproportioned bindings. That is, those that are not efficient in their current proportion (size, weight or other features), being therefore not endurable even when restored.
A few examples of the use of endpapers against the grain directionare discussed (both in the ancient times and more recently) as a probable way to deal with the weakness of the joint. It is likely taht experienced bookbinders used it on purpose to prevent a premature detachment of flyleaves.
The hypothesis highlights the benefits of sewn attachments in flexible areas as opposite of adhered ones. Whenever sewing is not feasible, the grain direction shall provide a structural nature to some extent, noteworthy for adhered movable unions.These ideas held in the past are to be considered in the future for ever complex decision making of book conservation.