 The library's preservation and conservation department's job is to make sure the library's physical collections are usable. For circulating collections, some other books are being put along the spine or have degraded leather, but they're otherwise structurally sound. To help hold it together, they're given a colibri jacket. This clear polyethylene book jacket keeps the spine intact without doing a more interventive repair. While this is a great option for most circulating materials with these damages, the process is limited by the opening range of these covers.