A method of making a molded resin product includes the steps of (i) providing a plurality of liquid resin components that each include a reaction monomer for a resin, wherein at least one of the liquid resin components includes a catalyst, at least one of the liquid resin components includes an activator, and at least one of the liquid resin components includes thermally expandable microspheres, (ii) mixing the liquid resin components; and (iii) injecting the mixed liquid resin components into a mold at a predetermined temperature. The predetermined temperature is at least 10° C. lower than an expansion start temperature of the thermally expandable microspheres.