Provided is a refrigerator including a cabinet having a refrigerating compartment and a freezing compartment defined therein and an ice maker disposed in the freezing compartment. The ice maker includes a cold-air hole for receiving cold air, an upper tray made of an elastic material, wherein the upper tray is positioned to be exposed to the cold-air flowing from the cold-air hole, a lower tray made of an elastic material, wherein the lower tray is coupled to the upper tray to define a plurality of spherical ice chambers therebetween, a driver for pivoting the lower tray to open the spherical ice chambers, at least one thermally-insulating portion formed at a top face of the upper tray and corresponding to at least one of the ice chambers respectively, wherein the at least one thermally-insulating portion is constructed to prevent the cold-air from invading the at least one corresponding ice chamber.