Choosing between acid-free boxes and plastic sleeves for a family archive is not an either-or decision — both have specific roles and work best when used together. The confusion arises because archival supplies are sold with similar-sounding descriptions but different chemistries, and not all products labeled ‘acid-free’ provide the same long-term protection. Understanding what each type of supply does, and for which materials, removes most of the guesswork.
What acid-free actually means
Acid is the primary chemical agent that yellows and weakens paper over time. Wood-pulp paper contains lignin, which breaks down into acid compounds. Acid from one document migrates to adjacent documents, accelerating deterioration. Acid-free materials have a pH of 7 or higher and do not contribute additional acid to their contents.
Lignin-free is a related property: materials described as acid-free and lignin-free will not generate acid through lignin breakdown over time. Buffered materials add an alkaline reserve — typically calcium carbonate — that neutralizes any acid migrating from adjacent items. For paper and photographs, buffered storage is preferable to simply acid-free. For photographs, a neutral (non-buffered) or slightly acidic environment is sometimes recommended by manufacturers — check the specific guidance for the type of photograph you are storing.
What acid-free boxes do best
Acid-free boxes provide physical protection and an enclosed microenvironment. They shield contents from dust, light, physical impact, and the handling pressures of stacking. An archival box also creates a buffer against short-term humidity fluctuations — the board absorbs and releases moisture more slowly than the contents inside, damping the swings that would otherwise cause paper to cockle and photographs to curl.
Boxes are the right choice for storing multiple items together as a collection: a set of letters from the same correspondence, a complete photograph album, or all the documents relating to a single person. They provide structural support for items that would otherwise flex and curl in a sleeve.
What plastic sleeves do best
Archival plastic sleeves — polyester (Mylar), polypropylene, or polyethylene — allow visual inspection without handling. They are chemically inert (polyester most so) and provide a physical barrier between the document and its environment. A sleeve protects against fingerprints, abrasion, and small amounts of liquid contamination from handling.
Sleeves are the right choice for individual items that will be handled or viewed repeatedly: a frequently referenced photograph, a framed document that needs to be removed and replaced, or a negative strip. They are also the correct housing for items that need to be separated within a box — individual letters in a folder, or negatives in a multi-pocket preserver.
Which materials need which housing
Paper documents: buffered acid-free folders in acid-free boxes. The folder provides separation from adjacent items; the box provides physical and environmental protection. Interleave particularly acidic documents (newspaper clippings, older documents) with buffered tissue.
Photographs: individual polyester or polypropylene sleeves in an acid-free box. For colour photographs, use neutral (non-buffered) sleeves; for black-and-white prints, buffered tissue interleaving is acceptable and may provide additional acid protection.
Negatives and slides: polyester negative preservers in an acid-free box, or polypropylene slide pages in an archival binder stored in a box. Never PVC.
Bound volumes: acid-free clamshell or phase boxes, with acid-free tissue interleaving between pages.
The practical summary: plastic sleeves protect individual items from handling; acid-free boxes protect collections from the environment. Both are needed for a complete storage system.
What to avoid
PVC (polyvinyl chloride) sleeves are among the most damaging materials for photographic and paper archives. PVC releases hydrochloric acid and plasticizers as it ages, which attack adjacent materials. PVC is often used in general office document wallets and photo albums. Test for PVC with a simple smell test: PVC has a faintly chemical or ‘new car’ smell; archival polyester and polypropylene are odorless.
Generic cardboard boxes — including most shoeboxes and document storage boxes sold by office suppliers — are acidic and should not be used for long-term storage of photographs or paper documents. Buffered archival boxes cost more but last significantly longer and do not damage their contents. The long-term cost of buying non-archival boxes is re-doing the work when the materials degrade.
Practical purchasing guidance
Reliable archival suppliers include Gaylord Archival, University Products, Hollinger Metal Edge, and Conservation Resources in North America; Preservation Equipment Ltd in the UK. General craft or office supplies stores rarely carry genuinely archival materials. When purchasing, look for explicit statements of pH neutrality or alkalinity, lignin-free construction, and a PAT (Photographic Activity Test) pass for materials that will contact photographs.
For a modest family archive, a starter set consisting of a flat archival box, a pack of acid-free folders, a pack of polyester sleeves for photographs, and a roll of acid-free tissue covers most situations. Expand the supply list as the scale of the project becomes clear.
Digitising as a complement to physical storage
Physical storage and digital backup are complementary, not alternatives. Acid-free housing slows the deterioration of originals; digital copies preserve the content independently of the physical condition of the original. A document stored in perfect archival conditions but never digitised is still at risk from a fire, flood, or other disaster. A document scanned at low resolution and stored carelessly loses quality each generation of re-scanning.
A good working standard: store every physical item in appropriate archival housing, and maintain a digital copy of everything with historical significance on at least two separate storage media.
Worth remembering: Use acid-free boxes for physical and environmental protection of collections, and archival plastic sleeves for individual items that will be handled repeatedly. Avoid PVC sleeves and generic cardboard boxes. Physical storage and digital backup work together — one does not replace the other.
Common questions
What format or settings should I use?
For physical storage, use buffered acid-free folders in acid-free boxes for paper, polyester or polypropylene sleeves for photographs and negatives, and acid-free clamshell boxes for bound volumes. Avoid PVC in all applications.
How should I label the files or items?
Label the outside of archival boxes with contents, date range, and owner. Label individual folders with document type, date, and name. For plastic sleeves, attach a small label to the sleeve rather than writing on the plastic, which can indent the surface against the photograph.
How many backup copies should I keep?
For digital copies of all physically stored items: three copies on two different media, with one off-site. For physical originals: one archival set in the best available conditions. There is no need to make multiple physical copies of originals — the digital backup serves that function.