A foaming composition useful to make an extruded foam is comprised of comprising a plurality of chains of a copolymer of one or more vinylidene aromatic monomers and one or more unsaturated acids, the copolymer having about 0.01 to about 15.0 percent by weight of the one or more unsaturated acids wherein the acid groups are pendant from the copolymer a metal salt, metal oxide or combination thereof, the metal having a valence of at least 2; and one or more blowing agents. The foaming composition may be made into a foam by heating the foaming composition to a temperature sufficient to melt and ionically crosslink said copolymer which is then extruded through a die forming a foam. The foam is comprised of an ionically crosslinked aforementioned copolymer, wherein the copolymer is crosslinked through ionic bonds between the unsaturated acids and the metal of the metal salt or metal oxide.