Solventless siloxane epoxy-based coating compositions for use on metals, plastics, wood, and glass are disclosed. The compositions are cationically curable in air by U.V. or by electron beam radiation. The siloxane epoxy coating compositions exhibit excellent film properties after curing, such as good adhesion, flexibility, and appearance. The coating compositions may be clear or may contain fillers, dyes, and pigments. A method for manufacturing a coated metal, plastic, wood, or glass substrate using the compositions is also disclosed, as well as the coated material manufactured by the method.