Medieval manuscripts were primarily composed and written on parchment or vellum, i.e. animal skin (typically sheep or cow) rather than papyrus, or paper. As it is written on animal skin, it may be easier to think of it as more akin to leather rather than modern paper. Medieval manuscripts are therefore remarkably well preserved and able to withstand degradation over the centuries. Unfortunately, it’s also why they were so expensive to produce! Each page represents a good deal of labor in drying, curing, scrapping, stretching, etc.

If you’re interested in learning more about the process, check out an accessible and updated classic on medieval manuscripts - Christopher de Hamel’s “Making Medieval Manuscripts” (2018).

Fun fact! If you are able to qualify and work through the labyrinthine bureaucracy of archives to access a medieval manuscript, you can often hold and touch them without gloves because they are so durable. I can personally attest having been to several archives, including Hill Monastic Manuscript Library in Minnesota, the Bodleian in Oxford, and the Bibliotheque Nationale de France in Paris.

Here is one example of such a handy policy from the Ransom Center of Medieval and Early Modern manuscripts: https://docslib.org/doc/8899795/safe-handling-of-medieval-and-early-modern-manuscripts