Two wipes can both be described as low particle and behave completely differently on a critical surface. The reason is that "low particle" is not one measurement. Liquid particle counting and fibre release test different things, under different conditions, and a report that presents only one of them is only half a specification.
This note explains what each test actually does, where the numbers can mislead, and how to use them together.
What liquid particle counting measures
A known area of wipe is agitated in filtered water under controlled conditions. The water is then passed through a particle counter, which reports counts by size channel. The result is a number of particles per unit area or per volume, usually dominated by sub-10 µm debris.
It is a good test for loose contamination on the cloth: dust from converting, fibre fragments, packaging debris. It is less good at predicting what happens when the cloth is rubbed against a surface, because agitation in water is not abrasion.
What fibre release measures
Fibre release counts the filaments a wipe sheds under a defined mechanical action. The result is usually expressed as fibres per square metre or per wipe, and it is the number that correlates with the visible lint you find on a dark surface after cleaning.
A wipe can pass a liquid particle count and still release fibres, because the fibres are attached until the cloth is worked. That is why a report showing only LPC is not sufficient for an optics or semiconductor application.
Where the numbers mislead
- Sample preparation. A result measured on a dry, unused wipe says little about a wipe that has been wetted and wrung.
- Water quality. The background count of the test water sets a floor. A very low result may reflect clean water more than a clean cloth.
- Size channels. A count dominated by particles below 5 µm can look impressive while the 25 µm fraction, the one that matters for a scratch, is not reported.
- Edge finish. Cut edges release more than sealed edges. A test on a sealed-edge sample does not qualify a cut-edge variant of the same cloth.
| Question | LPC | Fibre release |
|---|---|---|
| Is the cloth clean as supplied? | Yes | Partly |
| Will it lint when rubbed? | Not reliably | Yes |
| Does it predict surface scratches? | No | Indirectly |
| Sensitive to edge finish? | Somewhat | Strongly |
Which to ask for first
Start with fibre release if the surface is inspected optically: optics, displays, wafer edges, precision bearings. Start with LPC if the concern is contamination carried into a liquid process or a cleanroom environment rather than visible damage.
For a critical specification, ask for both, on the same lot, with the test method and the sample conditioning stated. Then ask one more question: was the sample taken from the production lot or from a laboratory batch? The answer decides whether the report describes what you will receive.
Test frequency and lot release
Qualification is not a lot-release test. Once a reference is qualified, routine release can rely on the supplier's certificate plus periodic verification — typically one lot per quarter, or after a converting change. Re-test earlier if a defect trend appears. The point is to know which number would change your mind, and to measure that number often enough to see it move.
Sealed-edge knitted polyester such as W2201 is the usual starting point where both numbers matter. For dry, delicate work, P2301 offers a different balance of absorbency and release.
Putting the numbers in a specification
Write the requirement as a method plus a limit: fibre release by a named method, below a stated count; LPC in a stated size channel, below a stated count; edge finish sealed; lot number recorded. That sentence is auditable. "Low particle" is not.
Then keep the report with the lot. If a customer asks why a batch behaved differently, the test record is the only way to answer without re-testing the whole warehouse.
Is a lower LPC always better?
Not automatically. A very low count can come from a tightly woven cloth that releases particles slowly but scratches a soft surface. Match the test to the failure mode you are trying to prevent.
Do I need to retest every lot?
Test on qualification and on change. Routine lot release can rely on the supplier's certificate plus periodic verification, provided the specification is written against a method.
Does a sealed edge eliminate fibre release?
It reduces it substantially by removing the cut filament ends. It does not eliminate fibres broken during use, which is why the mechanical action in the test matters.
Ask us for both reports on the same lot, and we will show you the method behind each number.
