The third main binding style is the detchōsō (oriental style binding). Sheets of paper are folded in the middle, placed on top of one another and pasted together near the fold. Their distinctive characteristic is that the pages that are glued together open only partially whereas those that are not open fully. The set of books known as the Sanjūjō sasshi which the famous monk Kūkai brought back from China in 806 were bound with this method. It is believed to be the most ancient of the book-style formats. Its main shortcomings are that the glue tends to come off easily and that books in this format are prone to being eaten by insects. (See Below)
Because of these problems, the method fell out of favor after the 13th century (the Kamakura era, See below), with the exception of the Shingon sect of Buddhism, which continued to use it into the modern period. Books in this format are also counted in booklets (jō).