Swell (bookbinding)

In bookbinding, swell refers to the increased thickness of a textblock along its spine edge after sewing. Swell is a function of the number of sections in the book, the kind of paper used, the style of sewing, and the thickness of the sewing thread. Human factors also influence swell, especially the force with which the bookbinder "bones down," or flattens, each section after sewing.