NonWood Panels used in Exhibit Case Construction

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Contributors: Members of the MWG's Materials Fact Sheet Working group, Jenifer Bosworth, Anne Ennes, Lisa Goldberg, Jamie Gleason, Jennifer Herrmann, Nancy Lev-Alexander, Patricia Silence, Catherine H. Stephens, and Theresa Voellinger
=== Introduction ===
The focus of this Tech Note is the use of non-wood panels in the construction of the case interior within an exhibit case and not the exterior portion of the case or gallery cladding for aesthetic reasons. 
Avoid wood products within an enclosed exhibit case when objects sensitive to acids are on display. However, for instances when other alternatives are not possible or when plywood and other wood composite boards are found in an existing case, see the Tech Note on wood-based panels for a discussion about the use, risks, and potential mitigations when including wood/composite wood product panels in exhibit cases. For information on high pressure, cellulose-based laminates as barriers, see the Tech Note on Laminates.
=== How are non-wood-based panels used in exhibits, especially in enclosed cases (display chamber plus areas that share air, e.g. silica gel compartment)? ===
Panels composed of a range of materials are used to construct interior walls, display decks, display chamber furniture such as risers, vertical mounting panels, and other object supports. These panels are also used to construct silica gel or other compartments that share air flow with the display chamber.
=== Why are non-wood-based panels a preservation concern? ===
Panels formulated from a variety of plastics have been considered or used as alternatives to wood or laminate boards. While some plastic panels are a safe preservation alternative to wood, others may offgas harmful volatile compounds; plasticizers and heat stabilizers are two components that are known to offgas compounds that are damaging to many types of collection materials. For examples, see references listed below.
Review recent testing results and other available information, especially because similar products don’t necessarily share the same chemical composition. For example, Komacel and Komatex, both extruded by the same manufacturer, present different risks to collections. The former is typically considered a safer choice while the latter offgasses volatile sulfur compounds that are known to damage cultural heritage collections. Consult recent research on PVC boards (in Additional Resources). 
Use the most recent material testing results because undisclosed formulation changes by the manufacturer can happen at any time. Testing and consultation with colleagues should be conducted regularly. Some test results are available on the AIC Wiki’s Material Testing Results. 
Be aware that acceptable polymeric materials may absorb/adsorb pollutants and then become secondary sources of offgassing. For example, polyethylene foam is considered inert but can become a secondary source for offgassing pollutants due to the environment where it was stored. 
Be mindful that the product you specify may be substituted with a similar generic product by a distributor. 
=== What types of non-wood-based panels can be recommended for use inside exhibit cases? ===
The MWG section of Cameo presents detailed information on a range of plastic construction boards and composite panels. Frequent testing or literature reviews should be done prior to selecting these panels.
Due to changes in technologies and formulations, as well as the variety of non-wood-based panels, recommendations are not straightforward, but product selection can be informed by current research. 
Non-wood-panels are fabricated from a variety of materials including PVC, polyethylene, polyurethane, polyester, metal laminates, and acrylic. More specific information about many of these materials can be found: Composite Board/Panels, Plastic panels.
Polymer/metal composite laminates (including Alucobond or Dibond), metal sheets, or acrylic panels are recommended for isolating wood-based products from the interior display or environmental chambers. These products can also be used to create microclimate chambers or silica drawers within a display case. 
If choosing PVC boards, see recent research for precautions on additives that may be harmful to cultural heritage objects. Less rigid boards such as Komacel have been found to be acceptable.
=== Preservation strategies ===
Review and research products carefully prior to use. 
Include metal, metal/composite or polymeric panels (acrylic, polycarbonate, polyethylene, polypropylene) as barriers to mitigate offgassing of other structural materials.
When using aluminized sheet or metal laminate film to create a barrier seal, aluminum tape or patches applied with heat or acrylic adhesive can be used to patch holes. This is a sustainable way to prolong the use of the barrier film through multiple exhibit rotations and a secondary way to use scraps.
Practical construction considerations include: 
 
* Some boards are more suitable for primary construction. For example thinner metal boards such as Dibond and Alucobond are very useful for cladding structural panels on the side exposed to collection objects (as they are considered stable). 
* Ethafoam 900 is almost as dense as wood and may be substituted as a structural support in some applications, especially in mounts or shipping crates.
* Some boards sag under weight when used in a horizontal position such as decking if not supported underneath. 
* The sheet size of some boards is very narrow, requiring multiple joints which are difficult to fashion. 
=== Additional Resources ===
Samide,. M. and G. D. Smith. 2020. "Assessing the Suitability of Unplasticized Poly(Vinyl Chloride) for Museum Showcase Construction" Journal of the American Institute for Conservation 61: 1-13.
Hatchfield, P. Pollutants in the Museum Environment
Products used in Preventive Conservation - Technical Bulletin 32 by Jean Tétreault