Barrer is a non- SI unit of gas permeability (specifically,

gas Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma). A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or ...

permeability) used in the membrane technology and

contact lens Contact lenses, or simply contacts, are thin lenses placed directly on the surface of the eyes. Contact lenses are ocular prosthetic devices used by over 150 million people worldwide, and they can be worn to correct vision or for cosmetic ...

industry. It is named after

Richard Barrer Richard Maling Barrer FRS (16 June 1910 – 12 September 1996) was a New Zealand-born chemist. His areas of research included gas permeability of membranes and zeolite science, of which he was a founding figure; he also gave his name to the zeo ...

Definition

\rm  \ barrer =  \frac

Here the 'cm³_STP' is standard cubic centimeter, which is a unit of

amount Quantity or amount is a property that can exist as a multitude or magnitude, which illustrate discontinuity and continuity. Quantities can be compared in terms of "more", "less", or "equal", or by assigning a numerical value multiple of a unit ...

rather than a unit of

volume Volume is a measure of occupied three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch). The de ...

. It represents the number of gas molecules or moles that ''would'' occupy one cubic centimeter at

standard temperature and pressure Standard temperature and pressure (STP) are standard sets of conditions for experimental measurements to be established to allow comparisons to be made between different sets of data. The most used standards are those of the International Union o ...

, as calculated via the

ideal gas law The ideal gas law, also called the general gas equation, is the equation of state of a hypothetical ideal gas. It is a good approximation of the behavior of many gases under many conditions, although it has several limitations. It was first stat ...

.
The cm corresponds in the permeability equations to the thickness of the material whose permeability is being evaluated, the cm³_STPcm⁻²s⁻¹ to the

flux Flux describes any effect that appears to pass or travel (whether it actually moves or not) through a surface or substance. Flux is a concept in applied mathematics and vector calculus which has many applications to physics. For transport ph ...

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 Darcy's law is an equation that describes the flow of a fluid through a porous medium. The law was formulated by Henry Darcy based on results of experiments on the flow of water through beds of sand, forming the basis of hydrogeology, a branch of e ...

.
In SI unit Barrer can be expressed as:

\rm  \ barrer =  \frac

To convert to CGS permeability unit, one must use the following:

\rm  \ barrer =  \  \ \frac

Where M is the molecular weight of the penetrant gas (g/mol). Another commonly expressed unit is Gas Permeance Unit (GPU). It is used in the measurement of gas

permeance Permeance, in general, is the degree to which a material admits a flow of matter or energy. Permeance is usually represented by a curly capital P: \mathcal. Electromagnetism In electromagnetism, permeance is the inverse of reluctance. In a magneti ...

. Permeance can be expressed as the ratio of the permeability with the thickness of membrane.

\rm  \ GPU = 10^ \ \frac
         =7.501\ \times \ 10^ \ \frac

Or in SI units:

\rm  \ GPU = 3.35\ \times \ 10^ \ \frac

References

Units of measurement {{measurement-stub