Water vapor permeability

Description

The ability of a material to transmit water vapor. Water vapor permeability is measured using the variable partial pressures of the water vapor on each side of the test material and changes are monitored over time. Water vapor permeability is usually given in the units of grams per square meter per day (g/m2.d). This indicates the number of grams of vapor that will pass through a square meter of the test material in one day. The thickness of the test material must be specified. A typical test thickness is 1 mil (1 thousandths of an inch thick). Some vapor permeability measurements are given as cc/m2.d, but in the case of water vapor, one cubic centimeter (cc) is equal to one gram. Vapor permeability is a measure of the affinity of the vapor to the substance and thus the vapors ability to diffuse through the substance. Since cellulose has a high affinity for water, it has a large water vapor permeability.

Synonyms and Related Terms

moisture vapor transmission (MVT)

Other Properties

Other units = grams per 100 square inches per day

Sources Checked for Data in Record

• Theodore J. Reinhart, 'Glossary of Terms', Engineered Plastics, ASM International, 1988

• Matt Roberts, Don Etherington, Bookbinding and the Conservation of Books: a Dictionary of Descriptive Terminology, U.S. Government Printing Office, Washington DC, 1982

• Pam Hatchfield, Pollutants in the Museum Environment, Archetype Press, London, 2002

• The Dictionary of Paper, American Paper Institute, New York, Fourth Edition, 1980