Blog – Document Recovery, Water and Storm Damage

Should University Libraries Use Vacuum Freeze-Drying or Desiccant Drying?

In the world of document recovery, vacuum freeze-drying and desiccant drying are among the top solutions when there’s water or fire damage. As a university library creates a disaster plan, it must determine which drying solution is best for their collections. By knowing the differences between the two, library staff can make an educated decision and improve communication with a disaster recovery service regarding its needs.

Facts about Vacuum Freeze-Drying

Vacuum freeze-drying involves using a low-pressure vacuum chamber to dry wet or frozen books and documents. As the vacuum runs, the temperatures remain below freezing so the ice crystals sublimate, vaporize without melting. Drying time varies between 1 and 10 weeks, depending on the wetness of the materials.


  • Works well for saturated books and documents
  • Dry small or large batches
  • No additional distortion or swelling occurs
  • Prevents pages from sticking together if document recovery techniques occur within the first six hours of the initial water damage
  • Prevents the need for rebinding
  • Lifts soot, dirt and mud to a document’s surface, making it simpler and less time-consuming to clean
  • Aids in odor removal
  • No need to remove encapsulating materials or polyester sleeves


  • The drying process does not occur on-site
  • Drying chambers have limited sizes (some chambers are quite large)

Good For

  • Saturated books and documents
  • Coated paper
  • Materials with water-soluble pigments and inks

Not Recommended For

  • Vellum
  • Some photographic materials
  • Leather

Facts about Desiccant Drying

Desiccant drying, or dehumidification, involves using a controlled chamber set at a specific temperature and air level, with a low relative humidity. The dryer’s dehumidifier traps and absorbs moisture by adjusting the dew point so that water no longer condenses. This drying method is best for damp and moderately wet documents and books. Drying times generally vary between two and five days.


  • If performed on-site, documents are accessible as they dry
  • If drying on-site, you can leave books and documents on the shelves
  • Drying on-site may help dry out the building overall


  • May cause documents and books to distort
  • Not a good option if books or documents have mold
  • You must remove documents and books from their sleeves
  • The process is more labor-intensive, as you must fan some books, interleave pages and spread out documents

Good For

  • Photographs
  • Film
  • Microfilm and microfiche
  • Negatives
  • Electronic media

Not Recommended For

Books and documents distorted by water
Saturated books and documents
Bound documents
Coated documents that aren’t interleaved

The best document recovery method for your university’s library depends on factors, such as:

  • The budget available for document recovery services
  • The time of year when the disaster occurs
  • The types of collections in the library or the type of collection affected
  • Preservation needs
  • The availability of staff

The decision to use desiccant drying or vacuum freeze-drying ultimately affects the success of your disaster recovery efforts. Depending on the media affected, the library may benefit from both technologies. Polygon is an international leader in document recovery. If you aren’t sure about which drying technology is best for your educational institution’s library, a Polygon representative can provide you with further details about the company’s restoration services and make a recommendation based on your needs.

[Photo from Arria Belli via CC License 2.0]

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