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I always use Polyethylene Terephthalate (PET) sleeves — Some people call PET "Mylar", but Mylar is a brand name of a special type of PET, Biaxially-oriented polyethylene terephthalate (boPET). The brand name I use is SafGard, from E&T Kointainer Company, the same folks who make KoinTains and SaFlips. I store the sleeved notes in red currency boxes available from many suppliers.
These materials in the table below have been classified as fine for archival storage. [ Last Update: Wednesday, 18-Sep-2013 16:11:14 EDT ] |
| Material | Description | Examples |
| Polyester | Polyester is a category of polymers which contain the ester functional group in their main chain. Although there are many polyesters, the term "polyester" as a specific material most commonly refers to polyethylene terephthalate (PET). | SuperSafe or holders made from Profar Polyester |
| Polyethylene (food grade) | This includes Polyethylene Terephthalate (PET), and "Mylar" or other biaxially-oriented polyethylene terephthalate polymers. Amorphous Polyethylene Terephthalate, or APET, is transparent version of the polymer — The semi-crystalline version is opaque and white and is commonly used in food storage. Melinex 516 is an example of a Polyethylene Terephthalate (PET) film. | SafGard. Frame-A-Coin Currency Holders, PCGS Currency Holders, Lighthouse GRANDE and VARIO currency pages are "Mylar D" equivalent (See: PCGS Currency Holders "Take the Heat") |
| Polystyrene | Polystyrene is an aromatic polymer made from the aromatic monomer styrene, a liquid hydrocarbon that is commercially manufactured from petroleum by the chemical industry. Polystyrene is one of the most widely used kinds of plastic. | BCW Currency Slabs |
| Polypropylene | Polypropylene (PP), also known as polypropene, is a thermoplastic polymer used in a wide variety of applications including packaging, textiles (e.g. ropes, thermal underwear and carpets), stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, and polymer banknotes. An addition polymer made from the monomer propylene, it is rugged and unusually resistant to many chemical solvents, bases and acids. | UltraPro Banknote Holding Ring Binder Display Pages, BCW Polypropylene Pages |
| Plexiglas | Plexiglas is a trade name for Poly(methyl methacrylate) (PMMA). It is sold under many trade names, including Policril, Plexiglas, Gavrieli, Vitroflex, Limacryl, R-Cast, Per-Clax, Perspex, Plazcryl, Acrylex, Acrylite, Acrylplast, Altuglas, Polycast, Oroglass, Optix and Lucite and is commonly called acrylic glass, simply acrylic, perspex or plexiglas. So, "hard acrylic" holders should be ok. | Collector Safe, Capital Plastics Currency Holders, Image Guard Currency Holders |
| Barex® | Barex resins belong to a family of acrylonitrile-methyl acrylate copolymers (AMAB) and offer high barrier properties to gases such as oxygen and nitrogen, as well as outstanding chemical resistance and inertness. | PMG Holders |
I would be suspicious of anything generically called "plastic", "acetate", "vinyl", or "PVC" (even if the PVC contains no plasticizers or stearates) holders. Sometimes, though, with a little research, you may find the "hard plastic" currency holder is made of acrylic or polystyrene, which should be fine.
The Library of Congress Preservation Web site indicates:
 Update on Acceptance of Polyester Film Products for Use in Encapsulation of Paper Artifacts (Revised October 22, 2004) Over the past several months, we have tested several biaxially oriented polyethylene terephthalate (PET) polyester films and found them to be satisfactory for use in encapsulation of paper artifacts. The acceptable films are:
To the best of our knowledge, all of the tested films, with the exception of Melinex type KL and type KM films, are coated for slip on one or both sides for ease of handling. The two uncoated films are available in very small thicknesses, 92 gauge for Melinex® type KL and 48-200 gauge for type KM, which conservators may find limiting for many applications (100 gauge equals approximately 1 mil or one thousandth of an inch). While we would generally prefer uncoated stock to eliminate any chance of an unforeseen interaction with the artifacts being encapsulated, we do realize that most processors find slip coating to be essential for ease of handling. Moreover, most such coatings are highly stable.
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Vendor Notes
Tom Denly indicates:
"Mylar D is a Brand name owned by Dupont plastics. It is truly a true polyester with an alignment of the molecules in long straight runs. The true reason Mylar D is so good is that it is made to an American Society of Testing Materials standard of purity that is extremely tight. Many plastics are mixed with other materials which will lower its melting point to a point that it can be heat sealed, these additions are in some cases sulfuric acid, hydrochloric acid, many oils, and occasionally esters. If not mixed perfectly these additives can leach out of the polyester into the paper money.
You will find that our holders are made to the Standards of Mylar D for purity and therefore can not be heat sealed but are welded to form a perfect seal. Our holders are manufactured by computer driven machines such that each holder is exactly like the next.
When I first got into the holder business Dupont made Mylar D, ICI Corp made Melinex 121, and Three M made a third brand of polyester each to the same A. S. T. M standard. Three M stopped making the material as there was too much competition for the limited need for the material, Then Dupont bought ICI Corp and realized that why compete and ICI could make it all which it does now. So truly it is a Melinex 121 make to Dupont Standards and Dupont ownership."
Melinex 121 is now Melinex 516.