Mechanically bonded nonwovens are especially suitable for this function if the nonwoven thickness is at least 30 times larger than the selected opening size. This has been determined by inspecting mechanically bonded nonwovens which have been in service for relatively long periods of time. A thickness adjusted to the opening size allows a depth filtration and prevents the development of a filter cake at the interface between geotextile and soil which would reduce the water permeability. The water permeability of the mechanically bonded nonwoven adjusted to the soil is hence ensured in the long term.


A geotextile filter layer withholds solid components, whilst allowing liquids to pass almost freely perpendicular to the filter plane.
It is differentiated between the mechanical strength (soil retention capacity) and the hydraulic filter effectiveness both with the aim to achieve a water drainage with a minimum loss of pressure.

The requirements can also be fulfilled by a mineral filter. However, geotextile filter layers have proven to be the most suitable and economic alternative.

Like in mineral filter layers, the filter length of the geotextile filters (thickness of the geotextile) can affect the long-term mechanical and hydraulic filter effectiveness. Filters are mainly used in hydraulic engineering and drainage systems.