A golf ball includes an inner core and an outer core, both made of highly neutralized acid polymers. The inner core does not substantially include any fillers, while the outer core does include fillers. The outer core may include fillers in an amount of from about 17.% to about 30.7% by weight. The filler may be barium sulfate. The core made from the inner core and the outer core may have an unexpectedly higher coefficient of restitution.