Vapour permeability represents the rate of vapour transmitting through per unit area of a permeable material with certain thickness. It is measured at a required temperature, relative humidity and vapor pressure.

Vapour permeability is the measure of a material’s ability to transmit vapor through it. The greater the permeability of a material, the more rapidly vapour could pass through it.

Units and Measures

Vapour permeability of a material is assessed in terms of amount of vapour that permeates and its transmission rate.

Following are the units for measuring vapour permeability:

  • SI Units: perm-centimeter (g/24 hr•m2•mm Hg•cm) of the thickness
  • Imperial Units: perm-inches (grain/hr•ft2•in Hg•in) of thickness.

Useful References


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