Diane:  One product which was very popular in the mid to late 80's was
"Pyrell".  I do not recommend this foam product because it has been verified
that it does decompose and will adhere to whatever has been resting on it.
 It also turns to a dust like material, which can become airborne.  It is
gray in color and does come in various thicknesses.  It was most popular in
the Army Museum System and widely installed.  I understand most of the
museums are now removing it from their collections storage.  Product
literature was collected to examine its contents etc.  At that time, the
product was touted as the perfect liner.  As in all molecular and  biological
life-things will turn to dust sometime!  Sarah (Fort Dix Museum  Curator
1984-86,  Director Historic Speedwell)