Use
Marbig Heavyweight 75 microns.
20 years so far
No noticeable (visable) damage as yet.
Under lock and key in stable environment.
Quote:
I have Avery binders made 15 to 20 years ago that are much better than new "heavy duty" Avery binders made now. They changed the design likely to reduce cost.
Similar here in Oz, Marbig no longer in stock from major supplier,
The new option (J Burrows) lopped 10mm from the width of the front and back covers, leaving ones sheets open to damage.