Philip has developed open-spine structures with 'yokes', across the shoulders of the book, usually at head and tail. Yokes are made with vellum/leather laminates (the vellum being the inner lining), pared to a feathered edge at both ends and glued down on each side of the book leaving a 'quarter joint'.
The gluing of the head and tail yokes - or full length spine 'yoke' - on to the book leaves an unglued space of about 5 – 10mm (depending the on dimensions of the book) on the edge of the spine under the yoke, spreading the otherwise sharp hinge crease that occurs on a tight joint.
This structure ensures that the endpaper sections are reinforced and that the boards do not break down off the book as easily as with conventional tight-jointed hinges. Yokes may obviate sewn head or tail bands whilst providing a strong pulling point for those who like to remove a volume from a shelf-full of books by its headband-reinforced cap.