A letter from the front, a birth certificate, a hand-drawn estate map, a box of family photographs: paper and photographs can last for centuries if they are stored well, or yellow, tear and fade within a few decades if they are not. Most damage is slow and avoidable. It comes from handling, from acids in poor-quality packaging, from airborne pollutants and from the wrong plastics.
This guide is for archivists, librarians, museum and collections staff, framers, collectors and family historians. It explains what makes a film archival, why polyester is preferred to PVC and ordinary plastic sleeves, how encapsulation and sleeves work, and how to handle and store the things that matter to you.
What makes a film archival?
An archival film is one that can sit against a document or photograph for decades without harming it. In practice, that means a film with nothing in it that can migrate out: no plasticisers, no coatings, no surface treatments and no dyes. It should be clear, so the item can be read and photographed without being removed, and it should be stable, so it does not shrink, stretch or go brittle with age.
Clear, uncoated polyester (PET) meets those needs, which is why it is the standard choice for conservation enclosures. Our Polymex® archival film is free from plasticisers, UV stabilisers, dyes and coatings, so it is chemically inert in contact with paper, photographs and textiles. It is dimensionally stable and resists stretching and distortion, and it is a barrier against acidity and airborne contaminants, two of the main causes of paper and fabric deterioration. It is the same family of film used for many everyday products, but made without the additives and coatings that suit packaging or print.
Why polyester rather than PVC or ordinary plastic?
Many cheap sleeves, album pages and document wallets are made from PVC. PVC is usually softened with plasticisers, and over time those plasticisers can migrate out of the film, leaving documents and photographs sticky, discoloured or stuck to the sleeve. Some PVC also releases acidic compounds as it ages. Archival polyester contains no plasticisers, so there is nothing to migrate.
Polyester is also not the same as every clear plastic sleeve. Films treated or coated for printing, adhesion or anti-static properties are excellent for their own jobs, but they are not what you want touching an original. Our guide to polyester film grades explains the difference between treated, coated and untreated films.
For photographs, the recognised test for enclosure materials is the Photographic Activity Test, set out in ISO 18916. If you are buying enclosures for a photographic collection, it is worth asking whether the material has passed it.
Encapsulation and sleeves explained
There are two common ways to put polyester to work:
- Sleeves and folders. The item slips into a polyester sleeve, open on one or more sides. This suits photographs, letters and prints that are stored in boxes or binders and taken out to be viewed.
- Encapsulation. The item is placed between two sheets of polyester cut a little larger than it, and the film is sealed around the edges, usually by ultrasonic welding or with double-sided archival tape set back from the item. The item is held by the film and its own static, not by any adhesive, so fragile sheets can be handled, displayed and even bound into an album without being touched.
The most important difference between encapsulation and lamination is that encapsulation is reversible. Lamination uses heat and adhesive to bond film to the document, and it is very difficult, often impossible, to remove without damage, which is why it is not recommended for originals. To release an encapsulated item, you simply cut the seal and it comes out unchanged.
Two cautions. Because polyester carries a static charge, encapsulation is not suitable for items with loose, flaking or powdery media, such as pastel, charcoal or flaking paint, which the static can lift. And acidic or damaged paper is often best cleaned and deacidified by a conservator before it is enclosed.
What to use for what
| Item | Common approach | Watch out for |
|---|---|---|
| Letters, certificates and single sheets | Polyester sleeve or encapsulation | Remove paper clips, staples and rubber bands first |
| Maps, plans and posters | Encapsulation in heavier film, stored flat | Large items need stiffer film to support them |
| Photographs and negatives | Polyester sleeves, handled by the edges | Ask whether the enclosure has passed the Photographic Activity Test |
| Book jackets | A clear polyester jacket cover | Avoid covers taped to the book itself |
| Microfilm, microfiche and printed records | Polyester sleeves and enclosures in boxed storage | Keep away from heat and damp |
| Pastel, charcoal or flaking paint | Not polyester: seek a conservator's advice | Static can lift loose media |
Choosing thickness and format
Thickness is a balance between flexibility and support. Conservators commonly use film of about 75 to 125 microns (roughly 3 to 5 mil) for encapsulation and sleeves: lighter film for small, flexible items, and heavier film where the enclosure must support a large or heavy sheet. Our polyester film thickness guide explains microns, gauge and mil if your supplier or specification uses a different unit.
Polymex® archival film is supplied in rolls of varying widths and thicknesses, for making your own sleeves, folders and encapsulations, and we can supply it sheeted to size, interleaved with tissue to protect the surface.
Handling and storage tips
- Handle as little as possible. A clear enclosure lets people read and examine an item without touching it. The oils and salts on skin leave fingerprints that can etch photographs over time.
- Handle photographs by the edges, ideally wearing clean nitrile gloves, and support large sheets from underneath rather than by a corner.
- Keep conditions stable. Store collections somewhere cool, dry and dark, with steady humidity. Lofts, cellars, garages and outside walls see the biggest swings in temperature and damp.
- Protect from light. Polyester does not filter ultraviolet light, so keep items out of direct sunlight and use UV-filtering glazing for anything on display.
- Use archival boxes and folders around your enclosures, and avoid sticky tape, glue and self-adhesive labels on originals.
How PSG supplies archival film
We have supplied archival film for preservation since 1994, and our Polymex® archival films are used in some of the world's most prestigious libraries, galleries and government departments, and are recognised by leading museums, art houses and curators worldwide. Tell us what you are protecting, its size and how it will be stored or displayed, and we will recommend the film, width and thickness. Our page on archival polyester film for encapsulation sets out the specification in more detail.
Protecting a collection? Ask our team for a recommendation and a quote for Polymex® archival film in rolls or sheets.
Polymex® is a trademark of PSG.
