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Membrane pore size ratings refers to the size of a specific particle or organism retained by the filter to a specific degree of efficiency. Pore size also affects flow rate, back pressure, and the life of the filter.
The pore size of filter media is identified by the diameter of the particle that it can be expected to retain with a defined, high degree of efficiency. Pore sizes are usually stated in micrometer (μm), which equals one millionth of a meter.
Pore size ratings refer to the size of a specific particle or organism retained by the filter media to a specific degree of efficiency. Ratings can be stated as either absolute or nominal pore size.
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 Measurement of the smallest particle that a filter repeatedly retains.
An absolute pore size rating specifies the pore size at which a challenge organism of a particular size will be retained with 100% efficiency under strictly defined test conditions. Among the conditions that must be specified are: test organism (or particle size), challenge pressure, concentration and detection method used to identify the contaminant.
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Measurement of the smallest particle a filter retains typically at a 90-98% efficiency level depending on manufacturer's claim.
A nominal pore size rating describes the ability of the filter media to retain the majority of particulates at (90-98%) and greater than the rated size. Process conditions such as operating pressure and concentration of contaminant, have a significant effect on the retention efficiency of the filters.
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Application |
Pore Size (μm) |
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Mycoplasma removal |
0.1 |
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Liquid sterilization |
0.1-0.2 |
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<3 μm column packings |
0.2 |
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Clarification |
0.45-1.0 |
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>3 μm column packings |
0.45 |
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Venting |
0.2-0.45 |
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Prefiltration |
0.8-5.0 | |
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(1) Define your application requirements
(2) Select a compatible membrane
(3) Choose the most effective and efficient pore size | |
