a large range of polymers of any molecular weight blends of two or more polymers into which there may be incorporated conventional additives may be desired and the materials forming the base will be selected depending to a certain extent on the form of the coating examples of polymers suitable either alone or in blends are as follows polyolefins including copolymers of ethylene with propylene butene methyl acrylate ethyl acrylate methyl methacrylate ethyl methacrylate vinyl acetate vinyl chloride vinyl propionate carbon monoxide maleate fumarate and itaconic esters terpolymers of ethylene vinyl acetate and olefinically unsaturated monocarboxylic acids for example acrylic or methacrylic acids the partially neutralized varieties of polymers comprising acid groups for example ionomeric resins which generally are the ammonium or alkali or alkaline earth metal derivatives polyvinyl chloride vinyl chloride copolymers containing as comonomer vinyl acetate vinylidene fluoride dialkyl maleate or fumarate fluoro carbon plastics or rubbers including polyvinylidene fluoride copolymers of vinylidene fluoride and hexafluoropropylene terpolymers of vinylidene fluoride hexafluoropropylene and tetrafluoroethylene copolymers of vinylidene fluoride and 1 hydropentafluoro propene or a terpolymer containing these monomers plus tetrafluoroethylene nitrile rubbers acrylate rubbers and polysulphide rubbers natural rubbers synthetic rubbers such as butyl neoprene ethylene propylene rubber and the ethylene propylene non conjugated diene terpolymers silicone rubbers including those derived from dimethyl siloxane methylphenyl siloxane or methyl phenyl vinyl siloxane these rubbers preferably being 34 gum form 34 also 34 gum 34 polyesters 34 gum 34 polyamides and other polymers or copolymers in 34 gum 34 form for compounds having stress grading electrical characteristics.