Thank you for the information. I've checked the Filmoplast P and it is
1.0 mil -- pretty thin -- and I can't imagine finding something thinner.
It is acid free, archival, and is supposed to last.

Scotch Invisible Tape is another tape known to last. It is a lot thicker
(I did not measure it, but specs show it to be 2.2 mil) and I use it on
heavy duty repairs like leaders or if I have to join to parts of a roll
back together (crosswise).

I've got very little of the original archival tape left which came
in various widths down to about 1/16". This narrow stuff was great
for making repairs between tracks as it did not cover the holes, which
with wider tape would have required cutting the tape out of the holes
-- a lot of work.

You are correct in that if you have to run a bead of tape down the total
length on one edge, you've pretty much got to do the same with the other
so that the rolls tracks. But this does add a lot of bulk.

Regards,

Jim Quashnock
Wichita Falls, Texas