At a PLMS meeting at ALA Midwinter in Chicago, Merrily Smith reported that the Library of Congress's Research and Testing Lab had tested Mylar and polypropylene to find their effect on paper encapsulated between sheets of these materials. Naturally they found that the rate of deterioration was more rapid with higher temperatures and paper pH. Deacidification slowed the rate of deterioration, as night be expected.
Two other findings were much less predictable. The first concerned the size of the gap commonly left in a corner of the enclosure, to prevent the aging paper from "stewing in its own juices," a matter of debate in conservation circles for years. They found that the more of the edge was left open, the slower the paper aged.
The second of these two findings confirmed the recommendation of Tim Padfield, David Erhardt and Walter Hopwood, in their 1982 paper, "Trouble in Store" (IIC Preprints):
Until a general purpose, wide range, showcase pollutant absorber is developed we recommend, as an acid gas absorber, carbonate-buffered paper, laid in cases. The exposed surface area of absorber must be large.
At the Library of Congress, undeacidified paper that was encapsulated together with a sheet of buffered paper behaved the same as if it had been deacidified.