Dutch weaves are woven so tightly that you cannot calculate the aperture size in the normal manner. Instead we measure them slightly differently by rating them on their ability to remove particles of a specific size.

A filter marked as ’10 micron’ can capture particles as small as 10 micrometres and there are two methods that we typically use to calculate this: absolute rating and nominal rating for filters.

However, there is no standardised methods of testing, so filters of the same micron can vary between different manufacturers. Although generally, the absolute method will provide a more accurate calculation – and here’s why…

The absolute micron rating is calculated by measuring the size of the largest pore that a particle can pass through in the filter. This relies on the filters having a definable pore size, which is not always the case.

This is why we also use the nominal filter rating method. This method identifies the size of the smallest particles that have been retained be the filer. It does not provide an absolute rating because the actual pores of the mesh could be larger than the particle being tested. 

Need help finding the right filter for you? Read our technical guidance here.