In both types of Dutch Weave the sum derived from multiplying the number of weft wires in a given measurement by their diameter results in theory, on a specification with no open space.  Because the wires are driven together during the weaving process, the aperture size cannot be calculated in the normal manner. There are two methods by which the aperture size can be determined:

BUBBLE POINT TEST

The pressure required to pass air bubbles through the mesh (covered by a test liquid) is measured.  The average aperture size is then calculated by taking into account surface tension, liquid density, temperature and immersion depth.

GLASS BEAD TEST

A suspension containing glass beads is passed through the mesh - the diameter of the largest bead passing through is considered as the absolute micron retention.