In order to determine the puncture resistance of geotextiles used for separation, CBR plungers with standard, pyramidal and hemispherical tips were used on a wide range of fabrics. Shape factors for predicting failure load under rounded and angular aggregate from standard plunger CBR puncture tests are shown to be fabric-specific, and different from previously quoted values. Conventional methods of expressing deformation as elongation make comparisons difficult, and it is proposed that deformation be expressed by CBR plunger displacement at failure. A rupture index for puncture resistance classification using results from the standard plunger CBR puncture test, is proposed.