Interaction between soils and nonwoven geotextiles is very important in applications of these materials as filters in geoenvironmental engineering. Filters are often used to avoid the erosion of soils in contact with the filter without impeding the flow of seeping water through the soil. A nonwoven geotextile should retain soil particles while allowing seeping water to drain freely. Significantly, the mechanism of soil-nonwoven geotextile interaction is very complex due to the variety of soils and geotextiles. The design of geotextile filters requires a clear definition of the geotechnical characteristics to be achieved with geosynthetics. Numerous methods have been developed for the determination of the filtration compatibility of soil-geotextile systems. These include the gradient ratio test, the long-term flow test, and the hydraulic conductivity ratio test. Without any doubt, the gradient ratio test is the most popular for measuring the filtration behaviour of soil-geosynthetic systems. This article presents a laboratory method for the study of the interaction between internally unstable soil and needle-punched nonwoven geotextiles, with particular reference to the applications of these materials as filters. The need for improvements in laboratory tests for a better understanding of soil-nonwoven geotextile interaction and modifying filtration criteria for nonwoven geotextiles is highlighted. The obtained results show that geotextiles having the same pore size of openings may have different filtration behaviour.