Ten classes of electrical insulating papers, excluding varnished papers, asbestos papers, and papers used in the manufacture of cables. Limiting values for thickness, substance, electric strength, mineral ash, conductivity of water extract, heat-ageing (assessed by decrease of bursting strength or tearing strength) and freedom from conducting paths (capacitor tissue paper only). Ranges of values for tensile strength, tearing strength (optional requirements), oil absorption, air permeability and pH val ue. Test methods (including optional test for chloride content), methods of conditioning and heat-ageing appended.