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Barrer is a non-SI unit of gas permeability (specifically, gas permeability) used in the membrane technology and contact lens industry. It is named after Richard Barrer.


Here the 'cm3STP' is standard cubic centimeter, which is a unit of amount of gas rather than a unit of volume. It represents the amount of gas molecules or moles that would occupy one cubic centimeter at standard temperature and pressure, as calculated via the ideal gas law.

In SI units, 1 Barrer is equivalent to 3.34×10−16 mol Pa−1 s−1 m−1.
The cm corresponds in the permeability equations to the thickness of the material whose permeability is being evaluated, the cm3STPcm−2s−1 to the flux of gas through the material, and the cmHg to the pressure drop across the material. That is, it measures the rate of fluid flow passing through an area of material with a thickness driven by a given pressure. See Darcy's Law.