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Polyester Encapsulation[1][2] is a method of stabilizing paper-based objects by sandwiching the object between slightly larger inert films of polyester and sealing the edges together. In this method, the object is not directly altered in any way, unlike Lamination. The encapsulation material, and the methods to seal edges, vary by equipment and desired treatment outcomes. The method is an innovative Housings option for paper-based materials, particularly for oversize and fragile objects, and does not need to be replaced or removed for viewing. However, it is not an universally appropriate treatment, particularly for objects with Friable Media (see also Media Problems, and Matting and Framing: Insecure Media).

The goal of this chapter of the Book and Paper Group Wiki is to share information, comments, and experiences about methods of polyester encapsulation.

This chapter was created in April 2014 within the AIC Wiki as a place to record and share the collective knowledge of Book and Paper Group members on the topic on polyester encapsulation.

Contributors: Rachel Freeman, Katherine Kelly, Evan Knight, Bill Minter (via interview), Cher Schneider, please add your name here

Polyweld.JPGMapInBookInMylar.JPGUltrasonic Welder.JPGEncapsulated Poster.JPGLarge Encapsulated Poster.JPGPolyester Roll.JPG32512-ATR-ledger.jpgPolyester encapsulation minterf deacidification.jpgSpine-pocket-wrapper-01.jpeg

Copyright 2019. The Book and Paper Group Wiki is a publication of the Book and Paper Group of the American Institute for Conservation. It is published as a convenience for the members of the Book and Paper Group. Publication does not endorse nor recommend any treatments, methods, or techniques described herein. There is an ongoing project to update the BPG Wiki. We welcome contributions and feedback. If you would like to get involved in this effort, please contact the wiki team at [email protected].

Factors to Consider

There are a number of Factors to Consider prior to deciding to encapsulate an item. Treatment Context must be balanced with the manufacture and condition of the object itself (Object Characteristics), and the available resources (Materials and Equipment). Specific treatment applications may be altered or combined. Readers are encouraged to perform their own evaluation and research before putting to use any of the treatment recommendations and suggestions included in this chapter.

Treatment Context

A. Value of Object

1. Intellectual
2. Historic
3. Aesthetic

B. Use and Handling

1. Frequency
2. Exhibition

Object Characteristics

A. Primary Support

1. Material
a. Paper
b. Parchment
c. Other materials which benefit from the added support and protection of encapsulation, such as Palm Leaf or Papyrus

B. Non-Friable Media

1. Printed
2. Manuscript
3. Photograph

C. Weight and Size of Object

D. Condition of Object

Condition of object affects choice to encapsulate or choice of method.
1. Deacidification[3] prior to encapsulation? Or include an Alkaline Reserve sheet with the encapsulated material?
2. Difficulty of encapsulating non-flat objects.

Current Research

Encapsulated samples of newsprint deacidified by various methods in 1983, prepared by Bill Minter. CC BY-NC-ND

"The role of polyester film encapsulation - with and without prior deacidification - a study using long- term, low-temperature accelerated aging" by William Minter and John Baty, Research and Technical Studies Specialty Group Postprints, Volume 4, 2013, p186. From a paper presented at the AIC Annual Meeting, 2013, in Indianapolis, IN, and available for download from the link. A summary of the presentation is available through AIC's blog, written by Laura Wahl.

Materials and Equipment

Material for Encapsulation

A roll of Mylar®

Mylar®[4] (1950s) or Melinex® 516[5][6] are uncoated, translucent films made from Polyethylene terephthalate (PET), a thermoplastic polyester resin. They are often used to generically refer to encapsulation films, however, both names are registered trademarks owned by Dupont Tejjin Films. The true generic term for these materials are Polyester Film or Plastic Sheet. They are available in rolls or sheets.

  • Chemically Stable
  • Transparent
  • Adds Tensile Strength
  • Reduces Handling of Original Object
  • Range of Thicknesses. 2mil, 3mil, 4mil, 5mil, and others. Selecting the appropriate thickness of polyester for an object is essential for successful treatment.
  • Uniform Structure
  • Resists Mold/Mildew
  • Creates Environmental Barrier


Long-fibered paper can be welded or otherwise sealed to encapsulate paper-based objects.

Hollytex® is a spunbonded polyester sheet structured from continuous filament polyester fibers. Calendered for high tensile and tear strength.

  • Chemically Stable
  • Chemical Resistant
  • Air Permeable
  • Smooth
  • Not Sticking
  • Range of Thicknesses
  • Resists Mold/Mildew

Stabiltex? (Do people still use for encapsulation?)

Sealing Methods and Equipment

Ultrasonic Welding

Ultrasonic welding uses low-frequency energy pulses through a moving applicator-head to seal malleable materials together along a seam.

  • Welding head of open-throated machine
    Ultrasonic Welding machines are used to effectively seal polyester, polypropylene, and other malleable materials of various thickness for library and archival materials. The energy and speed of the machine can be adjusted to ensure an effective weld. Machines designed by Bill Minter are typically 48 inches wide, with 40 inches of working daylight and an open-throat. However, models have changed over time, and each is unique. There are also about 4 or 5 welders that are 6 feet by 6 feet, with closed throats.

One of the adjustable parts of the machine is the distance the welding head is from the table. Older machines utilize manual replacement of shims that vary in thickness while newer machines use a pointer or indicator that can be directly adjusted.

Frequency, and type of frequency, can be adjusted as well.

Bill Minter is the designer and fabricator of most of the welding machines in use in libraries and archives. He has designed, constructed, and set-up ultrasonic welders since circa 1981. The first prototype machine was demonstrated to Peter Waters at the Library of Congress in 1981, who placed the first order. Over time, the Library of Congress purchased newer machines, and the Boston Public Library has since acquired this model, the first production welder. In total, there are over 200 machines in use in the United States and internationally. Although unverified, a welding machine is said to have been installed in a Buddhist monastery with manuscript materials on the top of a mountain in Tibet, circa 2005.

  • Gutta-Cut


Most heat tools cannot not achieve temperatures high enough to fuse sheets of polyester film together, however the Polyweld Machine
Polyweld machine via ISU Website
can. It has three distinct disadvantages compared with the ultrasonic encapsulator: high heat has risks to objects; it can weld a seam only at the very edge of the film; and it has a rather limited width (60 cm).

Double-sided Tape

Double-sided tape encapsulation with adhesive creep

Pressure-sensitive Double Sided Tape can be used to seal edges, however, there are significant risks to this method as the safety and longevity isn't equal to that of heat or ultrasonic welding. Preservation issues that arise from tape in encapsulation are:

  • Difficult to remove all air from encapsulation
  • Unsightly borders
  • Adhesive creep - Sometimes causing object to adhere to edge of tape and causing further damage
  • Object movement - Object may slide into tape during handling and become stuck at edges or corners, requiring careful intervention to release from adhesive mass
  • Tape encapsulation quickly fails when the adhesive becomes wet
  • Eventual adhesive failure

Sewn Edges

Treatment Variations

Oversize or Rolled Objects

Large objects are not always easy to encapsulate. Only a handful of welding machines have a working opening larger than 40 inches.
Large poster encapsulated and tacked, through encapsulation at margins, to wall.

Partial Welding

  • Spot Welding
  • L-sleeves

Applied Encapsulation in Book Conservation

Post Bindings of Encapsulated Leaves

Modifications of a Basic Polyester Post Binding, Barbara Meier-James, BPG Annual, Vol 2, 1983.

Preserve & Protect: The Benefits of Polyester Encapsulation to preserve the John Larkin Smith (1882-1936) Scrapbook, Suzanne Sawyer, Emory University MABRL blog post, Jan 15, 2014. Retrieved 5/20/2014.

Hebert, Henry. 2011. "Sleeves and Posts: A Rehousing Option for Scrapbooks." Archival Products NEWS 16 (4). Accessed October 9, 2014. http://www.archival.com/newsletters/apnewsvol16no4.pdf

Description of a treatment where a scrapbook was disbound, the pages placed in polyester L-sleeves, and bound into a post binding. The advantages of this treatment are its low-cost, its use of polyester when one does not have access to a polyester welder, and the ability to remove each page reasonably easily from the structure.

Ruzicka, Glen. 1983. “Polyester Encapsulation in Signatures.” The Book and Paper Group Annual 2.

Describes a method of creating a Remay hinge for folded encapsulations.

Encapsulation of Covering Materials

The Book and Paper Gathering has published detailed instructions for "A Spine-Pocket Wrapper for Books with Detached Spines"[7] made of Mylar. Spine-pocket-wrapper-01.jpeg Spine-pocket-wrapper-02.jpeg

Historical Techniques and Materials


Krueger, Holly. 2003. "Magnesium Revisited" Book and Paper Group Annual 22.
In addition to discussing the use of magnesium in deacidification treatments, this article reviews the history of silking at the Library of Congress from 1900-1940 and the reasons for its abandonment.

Cellulose Acetate Lamination

Krueger, Holly. 2003. "Magnesium Revisited" Book and Paper Group Annual 22.
In addition to discussing the use of magnesium in deacidification treatments, this article reviews the history of lamination at the Library of Congress from the 1940s to the 1960s and the reasons for its abandonment.

Double-Stick Tape Sealed Polyester Encapsulations

The result of housing paper materials between Mylar sheets adhered with double-stick tape


Canadian Conservation Institute, Encapsulation CCI-Notes 11/10

Stanley, Ted. Papyrus Storage at Princeton University The Book and Paper Group Annual 13, 1994


  1. http://cameo.mfa.org/wiki/Enapsulation
  2. http://www.conservation-wiki.com/wiki/Encapsulating
  3. http://cameo.mfa.org/wiki/Deacidification
  4. http://www2.dupont.com/Products/en_RU/Mylar_en.html
  5. http://www2.dupont.com/Products/en_RU/Melinex_en.html
  6. http://www.dupontteijinfilms.com/FilmEnterprise/Datasheet.asp?ID=117&Version=US
  7. Matsumaru, Mito and Stefania Signorello. November 8, 2018. "A Spine-Pocket Wrapper for Books with Detached Spines" The Book and Paper Gathering.

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