I refer the reader to the guidelines published by the US Library of Congress: http://www.loc.gov/preserv/supply/catissu.html
Originally Posted by Ryuji
The problem with paper envelopes is that they are not suited to handling as common to negatives in use. While the paper envelopes might be "more archival" with respect to the material triacetate they are less "archival" from the view of mechanical protection of the emulsion during any form of handling.
A good intermediate solutions, I think, is provided by Abodia: http://www.abodia.de/
What's interesting about the Abodia negative sheets is that the pockets are open and wide allowing for some air to circulate. The material is very thick, strong and clear so I suspect some form of polypropylene.
My procedure is to wrap negatives in endless triacetate sleeves--- built around the negative instead of as a pocket with its potential for damage posed by dust, grit or particles---- and to store these, increasingly, in Abodia hanging pockets. When I decide that negatives won't be printed anymore (at least not for a long time) I put them in envelopes in archival (mattboard) boxes.