A gasket (1) has a gasket core (2) and an outer gasket layer (4) covering the gasket core (2). At least one of the two sealing materials that make up the gasket has two reactive components before they are extruded, with said components chemically reatcting with one another as they are combined and/or extruded. The extruded core may be formed of a two-component resin which is at least one of an elastomer and a foam. The flexible outer layer may be a synthetic resin which is at least one of an elastomer and a foam. The outer layer may be electrically conductive, ultra-violet resistant, or resistant to the environment in which the gasket is to operate. Also taught are methods of apparatus for the manufacture of such gaskets