Selection guide / μm / nm
Filter Ratings: Define Before You Compare
Unit conversion is only the beginning
1 μm equals 1,000 nm. Even after converting units, compare rating definitions, test methods and retention efficiency. Equal numbers do not necessarily mean equal process performance.
Distinguish test conditions
Check the test fluid, challenge material, flow, differential pressure and filter area. Gas-filtration ratings cannot directly substitute for liquid-filtration ratings.
Define the actual objective
Identify the components to remove and those to preserve, then establish sample testing and acceptance requirements.
Use a comparison table that preserves definitions
Place the stated rating, unit, challenge material, retention measure and test conditions in one row for each candidate. A nominal pore label and an efficiency measured with defined particles provide different evidence. Keep an undefined rating open for clarification instead of ranking the smaller number as automatically superior.
- Record the rating definition and test method for each model.
- Compare particulate, microbial and molecular-retention claims separately.
Connect the rating to the target sample
For a process that removes occasional agglomerates while preserving dispersed particles, compare size distributions rather than total particle counts alone. A method that cannot distinguish unwanted from useful material cannot determine whether filtration improved quality or removed a functional component. Establish the acceptance method before the trial.
- Define relevant size ranges and sampling locations.
- Retain unfiltered controls, filtered results and the method detection range.
This general guide does not replace controlled technical documents or validation under actual process conditions.
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