mil thick to about 25 mil thick films of the present invention comprise acid copolymer ionomers u201c ionomers u201d which are copolymers well known in the polymer art ionomers are ionic copolymers formed by copolymerization of an u03b1 olefin u2014 such as ethylene propylene 1 butene and other 1 unsaturated hydrocarbons u2014 with an unsaturated carboxylic acid such as for example acrylic acid methacrylic acid or maleic acid and optionally softening comonomers in which some portion of the acidic groups in the copolymer is neutralized with metal ions such as sodium or zinc as used herein the term u201c copolymers u201d can describe polymers obtained by copolymerization of at least two different monomer species the term u201c terpolymer u201d can be used to specifically describe a copolymer that is obtained from copolymerization of three different monomer species at least one alkali metal transition metal or alkaline earth metal cation such as lithium sodium potassium magnesium calcium or zinc or a combination of such cations can be the counterion that neutralizes the carboxylate anion of the salt particularly preferred are ionomers that are at least partially neutralized with potassium cations terpolymers can also be made from an olefin such as ethylene an unsaturated carboxylic acid and a softening comonomer such as an alkyl meth acrylate providing.