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The backing paper/leader and trailer paper is really quite complex and expensive stuff, and none of the film manufacturing companies have the capability any more to make it themselves.
This has been repeated a lot. However film rolls are more than 100 year old. 120 film is almost 120 years old. It can't be THAT complex, THAT advanced. George Eastman & his people invented roll film backing paper more than 120 years ago, with technology from 1900.
During those 120 years, several dozen different companies manufactured roll film: kodak, agfa, gevaert, capelli, ferrania, forte,.foma, negra, valca, Fuji, konica/Sakura, lucky, shanghai, ilford, ensign, perutz, GAF, adox, efke, svema, tasma, tura, OrWo, the list goes on and on.. I have counted 23 (twenty three) different brands so far.
Surely this paper was made by many many different factories, not by one factory closely guarding an esoteric secret.
Simon Galley at Ilford told us all this story of 120 paper being more expensive than the film and difficult to source etc, but i don't buy the story. There must have been some hyperbole going on. Surely right now only one or two companies are ready to supply the coveted 120 paper at reasonable cost and complying with all the quality standards. But this doesn't mean it's going to be that way forever.