Best Practices for Preserving Plastic-Based Media in Libraries

Walk into the non-book section of any library and you will find a quiet collection of plastic: vinyl records in their sleeves, stacks of CDs and DVDs, and boxes of overhead transparencies left over from an earlier era of teaching. These materials carry sound, video, software, and lecture notes that often exist nowhere else. The problem is that plastic is not the permanent, indestructible substance we once assumed it to be. In fact, conservators at major institutions have started calling some early plastics “malignant” because they decay and release acidic gases that attack neighbouring objects. Preserving plastic-based media is therefore not a one-time act of careful shelving. It is an ongoing practice built on controlled environments, gentle handling, and a clear understanding of how each format fails. This post breaks down the best practices for three of the most common plastic media you will manage: vinyl discs, optical media, and plastic films and sheets.

Why plastic media deserves special attention 🔗

Most preservation training focuses on paper and bound volumes, but plastic behaves very differently. Plastics are relatively new to collections, and many of them are deteriorating faster than the centuries-old paper and metal objects sitting beside them. The decay is driven by the same enemies in almost every case: heat, fluctuating humidity, light, pollutants, and physical stress. As plastics age, they react with oxygen, water, and pollutants, which leads to discolouration, embrittlement, cracking, and loss of flexibility.

A general rule from plastics conservation is useful to keep in mind across every format. Specialists recommend keeping plastics in a stable environment with temperature held around 20°C and relative humidity between roughly 30% and 50%, because sharp fluctuations in heat and humidity are especially damaging. Light, particularly ultraviolet, should be filtered or eliminated. With that foundation in place, each format adds its own specific demands.

Care and storage of vinyl discs 🔗

Vinyl records are surprisingly durable. Within the preservation community they are grouped as “grooved media,” and they are considered one of the most stable physical formats developed so far. That stability is conditional, though. Dust, foreign matter, heat, and pressure can all cause distortion and surface noise during playback. The goal of good vinyl care is to protect both the groove and the sleeve, since the cardboard cover is far more fragile than the disc itself.

Handling vinyl correctly 🔗

The single most important habit is to handle records only by their outer edges and the centre label. Fingerprints leave oils that attract dust and grime into the grooves. You should also avoid flexing or bending the disc, because the grooves scratch easily and even tiny scratches can produce cracking and hissing during playback. When a record is being played, it helps to use the turntable’s automatic mechanism rather than placing the stylus by hand, since an unsteady hand can scratch the surface. Keeping the turntable lid closed during play prevents dust from settling into the grooves.

Cleaning and storage techniques 🔗

For routine cleaning, a soft anti-static brush held gently over the surface while the record turns slowly is enough to lift loose dust. The turntable itself should be cleaned regularly so it does not transfer grime back onto the disc. Records should be stored vertically, standing upright like books, never stacked flat, because stacking places uneven pressure on the lower discs and encourages warping.

The storage environment matters just as much as handling. A practical target range is a temperature of roughly 13°C to 21°C with relative humidity around 30% to 55%. This is one reason a basement is a poor choice in many climates: it tends to be damp. Each record should sit inside an archival-quality inner sleeve rather than an ordinary paper one, and the whole package should be kept in a cool, dry place away from direct sunlight. For libraries seeking detailed protocols, the collaborative guidance compiled by the Library of Congress and allied sound-archive bodies remains the standard reference.

Optical storage systems: CDs and DVDs 🔗

Optical discs arrived as a replacement for both vinyl and magnetic tape, and they spread quickly through libraries as carriers for music, film, reference databases, and software. They are generally more reliable and durable than magnetic tape or grooved records, but this reliability is easy to overestimate. The data on a CD or DVD is read by a laser focused on a reflective layer, and anything that disturbs that layer or the dye beneath it can render the disc unreadable.

The growth and the hidden fragility of optical media 🔗

It helps to understand that not all discs are equal. Pressed commercial discs, the ROM type, store data as physical pits stamped into the polycarbonate. Recordable discs, the “R” and “RW” types, instead rely on a layer of photosensitive organic dye or a phase-changing metal alloy. Research has consistently shown that recordable media tend to degrade faster than pressed ROM discs. This distinction matters because so much of what libraries hold, especially user-burned discs of local content, falls into the more vulnerable recordable category.

The uncomfortable truth is that lifespans vary enormously. Studies, manufacturer claims, and anecdotal reports place the lifetime of recordable optical discs anywhere from a couple of years to more than 200 years. The deterioration is sometimes called “disc rot” or “CD rot,” and it occurs through oxidation, hydrolysis, and mechanical stress that increase a disc’s error rate until the data can no longer be corrected. When that error rate crosses the threshold set in the ISO standard for CD-ROM, the disc may become unplayable.

How to handle and label discs 🔗

A common mistake is treating the label side of a CD as the tough side. It is the opposite. On a CD the reflective metal layer sits very close to the label surface, so a scratch or dent from a pen or sharp object on the top can destroy the reflectivity below and permanently lose the data. Because of this, you should never write on the label side with a ballpoint pen or pencil. The safest practice is to mark only the clear inner hub of the disc, and if you must label the surface, use a non-solvent-based felt-tip permanent marker.

Discs should always be held by the outer edge and the centre hole, never touched on the reading surface. Other sound handling rules from the standard NIST and CLIR guide for librarians include returning discs to their cases immediately after use, storing them upright in plastic cases made for the format, and avoiding adhesive labels, which can unbalance the disc and whose adhesives may attack the layers over time. Leaving discs in their cases also shields them from sudden environmental swings.

Extending the life of optical collections 🔗

For storage, optical discs prefer cool, dry, and dark conditions, and accelerated-aging research found that rapid shifts in temperature and humidity reduce disc life. Direct light, organic solvents, and moisture should all be avoided. Where maximum longevity is the goal and budgets allow, conservation guidance points to a CD-R built with phthalocyanine dye and a gold metal reflective layer as the most stable recordable option.

The most important principle, though, is that no optical disc is permanent. Digital archiving experts widely accept that no carrier lasts forever, so data must be actively maintained and migrated to newer media before the old format becomes obsolete. One state archive guide recommends testing readability frequently and copying content to fresh media every three to five years. For any library, the lesson is that making and refreshing copies, not perfect shelving, is the real safeguard.

Plastic films and sheets 🔗

The third category covers the transparent plastic sheets used on overhead projectors, often called transparencies, viewfoils, or simply “acetates,” along with slides and other film-based materials. These sheets are typically made of cellulose acetate or, in later years, polyester. The distinction between these two plastics decides almost everything about how you preserve them.

The vinegar syndrome problem 🔗

Cellulose acetate is the more common and the more dangerous of the two. As it ages, moisture causes it to break down and release acetic acid, the same compound that gives vinegar its smell, in a process widely known as “vinegar syndrome.” The reaction is autocatalytic, meaning the acid it produces speeds up further deterioration once it begins. A decaying acetate sheet will often emit a sharp vinegar odour, and the material may shrink, become brittle, develop bubbles, or form wavy grooves called “channelling.”

The danger spreads. Acetate suffering from vinegar syndrome can infect other acetate items stored nearby, especially in poorly ventilated areas. Because the high relative humidity hastens this decay, you should isolate any item that smells of vinegar from the rest of the collection, store acetate in unbuffered paper sleeves rather than sealed polyester ones, and keep the storage area well ventilated so the acidic gases do not accumulate.

Caring for transparencies and avoiding warping 🔗

Polyester sheets, often sold under the trade name Mylar, are far more stable. Polyester is considered chemically inert and, if stored well, can last over 500 years. For ongoing collections, polyester is the safer material to retain, and reformatting deteriorating acetate onto a stable medium is a sensible long-term plan.

To prevent warping and physical damage in any plastic sheet, the priorities are stable, moderate temperature and humidity, and storage flat or properly supported so the sheets do not curl under their own weight or stick together. Stacking heavy boxes on top of transparencies invites distortion, much as it does with vinyl. The broader plastics-conservation rules apply here too: keep them in the dark when not in use, filter ultraviolet light, allow air to circulate, and check the collection at least once a year, separating any object that shows signs of degradation. For severe cases, conservators sometimes use vapour scavengers or molecular sieves such as zeolites inside enclosures to absorb the off-gassed acids.

Building a routine that works 🔗

Across all three formats, the same handful of principles keep reappearing. Control the environment with stable, moderate temperature and humidity. Keep light, dust, and pollutants away. Handle items by their edges, never their working surfaces. Store everything upright or flat as the format demands, never under pressure. And inspect the collection regularly so that early decay, whether a scratch, a warp, or a whiff of vinegar, is caught before it spreads. For optical media especially, accept that the carrier will eventually fail and plan to migrate the content forward.

None of this requires a laboratory. A clean, cool, dark, well-ventilated cupboard with archival sleeves and a yearly inspection schedule already places a small library far ahead of the slow damage that neglect guarantees. The plastic media in your care is essentially borrowed time, and thoughtful storage is how you extend the loan.

What do you think? Looking at the non-book materials in a collection you know, which format do you think is most at risk, and would you invest your limited budget in better storage conditions or in migrating the content to new media before the originals fail?

References

1. https://cen.acs.org/articles/89/i29/Preserving-Plastic-Art.html
2. https://en.wikipedia.org/wiki/Conservation_and_restoration_of_plastic_objects
3. https://www.nature.com/articles/s40494-026-02337-6
4. https://www.museumsassociation.org/museums-journal/in-practice/2019/04/15042019-plastics-collections-plastics-care/
5. https://info.gaylord.com/resources/best-practices-for-vinyl-records
6. https://archives.lacrosselibrary.org/blog/vinyl-preservation-like-a-record/
7. https://www.loc.gov/preservation/care/record.html
8. https://en.wikipedia.org/wiki/Optical_media_preservation
9. https://www.loc.gov/preservation/scientists/projects/cd-r_dvd-r_rw_longevity.html
10. https://www.canada.ca/en/conservation-institute/services/conservation-preservation-publications/canadian-conservation-institute-notes/longevity-recordable-cds-dvds.html
11. https://www.loc.gov/preservation/scientists/projects/cd_longevity.html
12. https://nvlpubs.nist.gov/nistpubs/legacy/sp/NISTspecialpublication500-252.pdf
13. https://www.clir.org/pubs/reports/pub121/contents/
14. https://apps.azlibrary.gov/files/docs/arm-guidance-media_storage_and_handling_of_long_term_and_permanent_records_12-29-2014.pdf
15. https://psap.library.illinois.edu/collection-id-guide/plastictransparencies
16. https://cool.culturalheritage.org/byauth/messier/negrmcc.html
17. https://plastiquarian.com/?page_id=14326