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The ability of a material to permit the flow of a Gas, Vapor, or Liquid through its pore spaces without any chemical reaction. Permeability is measured as a rate of diffusion and is a function of the pressure differential on each side of the material. The permeability of gases (Air, Oxygen, Nitrogen, etc.) is primarily dependent on the porosity of a substance, while water vapor transmission is dependent on the absorption of water into the material. Standard units for gas permeability is usually given in the units of milliliters per square meter per day (ml/m2.d). This indicates the volume of gas 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). Water vapor permeability is given as grams per square meter per day. The permeability of a rock is its ability to conduct liquid or gas. It is measured as the proportionality constant, k, between flow velocity, v, and the hydraulic gradient, i; v=ki.

See also Gas permeability, and Vapor permeability.

Synonyms and Related Terms

Permeabilität (Deut.); perméabilité (Fr.); permeabilidade (Port.); Examples: gas permeability; vapor permeability

Resources and Citations

  • José Delgado Rodrigues, LNEC, Submitted information, 2009.
  • ASTM, Standard Terminology of Microscopy, Annual Book of ASTM Standards, Section 14, General Methods and Instrumentation, ASTM, E175, 75-78, May 1982
  • Matt Roberts, Don Etherington, Bookbinding and the Conservation of Books: a Dictionary of Descriptive Terminology, U.S. Government Printing Office, Washington DC, 1982
  • Random House, Webster's Encyclopedic Unabridged Dictionary of the English Language, Grammercy Book, New York, 1997
  • The American Heritage Dictionary or Encarta, via Microsoft Bookshelf 98, Microsoft Corp., 1998
  • Rosalie Rosso King, Textile Identification, Conservation, and Preservation, Noyes Publications, Park Ridge, NJ, 1985