Deals with test procedures for evaluating water treeing in polyethylene (PE) and crosslinked polyethylene (XLPE) compounds, as a way of assessing their relative performance under alternating electric stress, in the presence of water. The two methods covered are: method 1, which deals with evaluating insulating materials, and method 2, which deals with evaluating insulating sandwiches which consist of insulating material in close contact with semiconducting screens.