Are different formats of film on different bases?

I used to think that 35mm film was thicker than 120, but I thought maybe it was just because 120 is so much wider that it only seems that way. I figured they were all cut out of the same big roll. But then I got into sheet film and sheet film seems way thicker than either 35mm or medium-format. If it's on a special base, it explains a lot of why certain companies (fuji) don't offer certain films in sheet sizes.

For the films that I use, 120/220 is the thinest, 135 is thicker, and sheet is the thickest.

Some sheet films are (were) on Estar bases. Some, I guess, are just thicker. Anyone who has tried to finesse 4x5 film from an EK film pack onto ss 4x5 holders and have it stay there during development surely appreciates the thickerer bases.

Before I developed some sheet film, I was all worried about needing a negative carrier with glass in it to prevent sagging. With as thick as this Foma 4x5 film is, it seems plenty stiff enough to stay flat by itself.

If you look at the manufacturer's data sheets for films (where they are available) you'll see that 35mm is normally thicker than roll-film, presumably because it has no backing paper and needs to be robust enough to be pulled through the camera's transport system. Sheet is even thicker than 35mm, presumably to give it rigidity because of its size.

When Kodak first introduced its T-Max 100 & 400 roll-films, they were on a noticeably thicker base than other roll films, which personaly I quite liked. But some people complained of difficulties in winding them through certain cameras. On the current data sheets, the thickness of the T-Max roll films seems to have been reduced somewhat.

Some roll films are now on a polyester base but I don't know how these compare in the thickness of the base to conventional roll films.

Some typical thicknesses


Spooled film

TAC (Triacetate)
135: 120μm
120: 95μm-115μm

PET (Polyester)
135: 100μm (converted from aerial film/or surveillance film/or microfilm)
135: 75μm (to make high capacity cassettes)
120: 100μm (converted from aerial film)


Sheet film

TAC
obsolete (200μm?)

PET
175/200μm

Why isn't sheet film on acetate?

PET has greater stiffness than TAC, which makes it better suited for sheet film
There are more superior characteristics, but they are of less importance for pictorial photography.

PET has also an inferior characteristic, its more permanent core-set behaviour, which means it is lesser attractive for making spooled film.