The idea of not completely sealing paper items in plastic enclosures
came from research that the Library of Congress undertook in the
late 70s/early80s. Their research showed that acidic paper
deteriorated more rapidly if completely encapsulated (ie. no gaps)
than unencapsulated paper, hence the recommendation that paper be
deacidified before encapsulating and that gaps be left at the corners
of the encapsulate.

However  from the point of disaster prevention
(potential water damage) it is preferable to seal objects completely
in archival quality enclosures.

Tamara Lavrencic
Collections Manager
Historic Houses Trust of New South Wales