The Archival Methods Film Storage System with Polypropylene Sleeves lets you "Sort" "Save" and "Secure" your valuable 35mm or 4x5" negatives and unmounted transparencies. What Archival Methods has done is put together several popular items from their catalog into kits that give you everything you need to simply organize and preserve large quantities of film. These convenient kits also preserve cash in that you save approximately 15% over the individually priced items.
Your films are put into the sleeves for protection, the sleeves are put into the folders or envelopes for sorting and cataloging, and these are stored in the box
Four kits are offered: two for 35mm (6-frame max.) negative or transparency strips and two for 4x5" negatives or transparencies
The difference is in the sleeves you select; polypropylene sleeves are safe and economical but lack optical clarity; polyester sleeves (what used to be called "Mylar") are crystal clear and more rigid and thus make viewing and handling your films that much easier and user friendly. But they cost more. If your files are accessed often, that would be the better way to go.