This is a structure developed by Ben Elbel and I learned it from Erin Fletcher.
Erin describes it as "an easy and economical form of bookbinding. The covers are constructed entirely from heavyweight paper, layered to create rigidity and strength, while the flexible spine allows the binding to open without constraints."
I used St-Armand paper for the covers which I decorated with some Sashiko embroidery. The book has 7 signatures with 4 folios of Mohawk superfine paper.