Medex (a form of MDF medium density fiberboard) though used for years for case interiors, has recently been failing oddy testing for chemical stability. The best bet is to make sure you have an adequate vapor barrier between the structural material you are using and the space that contains objects.
A well known material is called Marvelseal. Depending on the type, it is comprised of a couple of different plastics and all versions contain a very thin layer of metal foil.
Another option is to include an intercept type of material in the air space to absorb any contaminants. Traditionally this is activated charcoal and is often placed underneath the deck for easy maintenance (also a good place for silica gel if you need it).
It also comes in paper form that can be placed underneath fabric etc..
There are some especially nifty materials designed especially to protect metals also.

In terms of the actual sheet material used for construction, MDF is nice and rigid and has no end grain to worry about like regular plywood. It machines and takes paint well. The trade off is that it is quite heavy. 
Traditionally most cases and pedestals have been constructed with shop grade birch (sometimes poplar) plywood.
Good luck!

T. Ashley McGrew
Lead Preparator
J. Paul Getty Museum
1200 Getty Center Drive 
Los Angeles, CA  90049-1687
Phone 310-440-6424
Fax 310-440-7741
[log in to unmask]

>>> [log in to unmask] 01/20/05 06:16AM >>>
We are looking to fabricate some museum quality exhibit
cases for our front lobby.  

Does anyone know what is the best type of wood to use,
sealer, wood for the back, etc.?  I heard plywood is out
for backing because of outgasing.  I would appreciate your
views.  Thanks in advance.



John Martinson SRA-6117
Museum Specialist
Snake River Area Office
230 Collins Road
Boise, ID 83702-4520
Telephone: (208) 383-2287
Web: www.usbr.gov 

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