. . "It would be desirable to incorporate many of the desirable attributes of such other, non-rubber footwear products into a footwear vulcanizate while retaining many of a vulcanizate's desirable attributes, such as resistance to air, gas, sunlight, hydrocarbons, moisture penetration, fats and oils, and acid and other chemicals, together with its excellent durability, strength, elasticity, electrical" . . . . .