Why does the lining or outer stitching appear loose or puckered when the Techo cover is opened flat to 180 degrees?

The moment you place the planner on a desk and open it completely to both sides, it immediately catches your eye right at the inner fold. This is a natural phenomenon. Hobonichi's Techo covers are structured to open flat to 180 degrees on a surface, so the outer stitching area may pucker or the lining material may look loose^[1].

Covers made by layering thick cloth or leather have different circumference lengths drawn by the inner and outer fabrics between when they are closed and when they are fully open. When the book is closed, the outer fabric stretches and the inner fabric compresses; conversely, when opened flat to 180 degrees, the outer fabric becomes taut while slack remains in the inner fabric. Without this slack, the cover would not rest completely against the surface and would float up when the planner is fully open.

In fact, the guide for the Hiroko Kubota: The Sea’s Dream at Dawn [Large 5-Year Techo] cover also explains that due to the structural characteristic of opening flat to 180 degrees, the outer stitching area may pucker or the lining may lift^[2]. hmmm, it is essentially providing the necessary slack in the fabric so that the paper touches the desk evenly without having to force it down by hand.