The materiality of manuscripts is a relatively new field of study, which adds to an art-historical approach to bookbinding history, but also provides information on the cultural circumstances under which manuscripts were produced. With regard to structure and binding techniques, the Islamic bookbinding tradition is generally assumed to be a conservative one. The predominant manuscript structure is usually denoted as a case-binding, and bindings are roughly divided in two groups, those with and those without a flap. Close examination of a variety of manuscripts during conservation treatments in Leiden University Library, has resulted in a different view: there is much greater diversity to be found in the way Islamic manuscripts are sewn, and there is good reason to doubt the assumption that the covers are made as separate entities apart from the textblock. Moreover, several characteristics seem to point to somewhat isolated traditions. This paper discusses these issues and argues the necessity of a more refined classification of Islamic manuscript structures. To illustrate the differences one can find in Islamic manuscript structures, the material characteristics of Southeast Asian manuscripts will be examined in more detail.