The 120 film format is a roll film which is nominally between 60.7 mm and 61.7 mm wide. Most modern films made today are roughly 61 mm (2.4 inches) wide. The film is held in an open spool originally made of wood with metal flanges, later with all-metal, and finally with all-plastic. The length of the film is nominally between and , according to the ISO 732:2000 standard. However, some films may be as short as . The film is attached to a piece of backing paper longer and slightly wider than the film. The backing paper protects the film while it is wound on the spool, with enough extra length to allow loading and unloading the roll in daylight without exposing any of the film. Frame number markings for three standard image formats (6×4.5, 6×6, and 6×9; see below) are printed on the backing paper.