Drainage element acting as the geotextile allows free drainage of liquid through its thickness. The geotextile has a high water conductivity in the plane of the blanket, being proven in the case of filter drains or mattresses. By filing the geotextile is generated conducting fluids tend to rise toward the surface, care should be taken in this protection because the consequences can be those of Fig.

Mechanical requirements: To perform satisfactorily draining the thickness must be sufficient to increase the tension normal to the plane of driving.

Hydraulic requirements: The geotextile is to prevent the washing or transport of fine particles, which when deposited on it reduces its horizontal permeability kh. It must also ensure the transport of water in its plane without great loss of pressure.

Durability requirements: Avoid clogging the drainage system of the geotextile.