Filtration
Filtration functions to restrict the migration of fine soil particles from a soil mass while remaining permeable to water movement greater than, or at least equivalent to the permeability of the protected soil.
Drainage
Water is conveyed along the path of the geotextile due to its construction, and then to an outlet. Water may be vertically or horizontally conveyed. Drainage is related to the role of filtration, and is a function of the permeability of a geotextile and its pore opening size or porometry.
Separation
Separation is the function which prevents two distinct soils of different materials from intermixing. The key factors for a geotextile to satisfy this function are porometry, toughness and strength.