I think this subject actually came up years back when MMD was still in
its infancy.  In any event I have yet another set of pros and cons for
readers to consider!

What makes rubber elastic is its chemical nature.  In rubber, chains of
complex organic molecules are bound together by sulfur atoms.  Imagine
two wooden sticks with strings of rubber between them.  Then imagine
a sulfur atom in the middle of each string of rubber.  When the wooden
sticks are pulled in opposite directions, the sulfur-to-organic bond is
stretched.  There happens to be a certain amount of bond elasticity in
the organic-sulfur atom-organic linkage.  That's a very rough model of
what makes rubber elastic.

Over the years, air and moisture eventually react with the sulfur atoms
and hence the bonds are broken.  That's the end of the elasticity and
of course the band itself.  What's usually left is a mess of organic
"goo" or rock-hard cement-like material.

There is one thing _not_ to do, and that is to spool a roll with a
rubber band in contact with the metal ring tab.  Over the years trace
amounts of moisture reacting with sulfur can produce sulfuric acid and
attack the ring and destroy the band at the same time.  I'm sure
readers can recall removing rubber bands where the band was slightly
"stuck" to the metal tab more than to the rest of the roll.

If rubber bands are used (and I confess to still using them!) please
never allow them to cover an original roll label.  I always put them to
the side of the label.  So many times I've seen a label destroyed from
the removal of a decomposed rubber band, leaving a vertical channel of
torn paper through the label.

So, there are a few technical points which unfortunately argue strongly
against the use of rubber bands.  Other materials which MMD readers
have proposed are far safer.  A cloth tie is one good solution.  In my
experience the rubber bands always decompose within 10-15 years or so.
But old habits are hard to break, and I still use the rubber bands on
every roll (albeit not in contact with a label or metal pull-tab)!

All best,
Frank Himpsl
http://www.http:valleyforgemusicroll.com/