D.Babson,
The 2 mil bags are not good because after opening and closing them about ten
or fifteen times, they don't seal as well as the 4 mil bags. Of course, if you
simply intend collections to be dead storage and not used for research then 2
mil might make sense. But many artifacts require conservation, change of the
insert tags, and should be available for examination. Having spent fifteen
years working with historic artifact collections at the Fort Guijarros Museum
Foundation Lab, I can attest to the issue. I believe that is why the National
Park Service requires 4 mil bags.
Ron May
Legacy 106, Inc.