Prior to the war, compounds made from natural rubber were used for cable insulation and protective jackets far in excess of any other material. This widespread application of rubber was the result of many years of development in compounding and processing technique, together with new methods for the evaluation of the improved properties of these new compounds. Rubber had become the accepted standard insulation for power cable from low-voltage building wires to 33 kv. submarine cable, communication wire, and sheaths for portable cords and cables. Neoprene sheaths and vinyl polymers (insulation and sheaths) had begun to find a considerable place in the industry despite their relatively higher cost. This was particularly true of flameproof shipboard cable for the U. S. Navy. The use of these materials in place of rubber for specific applications was fully justified because they were superior to rubber in certain respects, chiefly in oil, flame, and oxidation resistance, and stability in the presence of ozone or direct sunlight. In the case of vinyl polymer insulations, some sacrifices in electrical characteristics were necessary in order to obtain the above-mentioned physical properties.