Gerald C Koch
Member
The film base thickness was essentially determined when then film format was first designed. While one can certainly spool 135 film with a thinner base anything thicker than currently used will lessen the number of exposures on a roll. For 120 film remember that film and paper backing must both fit on the roll. In this case a thinner base that that for 135 film is required. For sheet film a base is required that will not make the sheets hard to handle so you don't want a thin floppy base.