 The needle punching method of manufacture (US patent filed in 1989) gave the resulting composite material shear strength, a critical feature for installation on slopes.Other names used for GCLs since their initiation are “clay blankets”, “bentonite blankets”, “bentonite mats”, “prefabricated bentonite clay blankets” and “clay geosynthetic barriers”, the latter currently favored by the International Organization for Standardization (ISO).The engineering function of a GCL is containment as a hydraulic barrier to water, leachate or other liquids and sometimes gases.