A four piece golf ball includes several relationships among the values of the densities of its layers. Namely, the sum of the density of the inner core and the outer core is at least 2 g/cm3, the sum of the density of the inner cover layer and the outer cover layer is at least 2.2 g/cm3, and the difference between these two sums is at least 0.1 g/cm3. The inner core is made of a highly neutralized acid polymer, the outer core is made of a polybutadiene rubber, and the inner and outer cover layers are made of a non-ionomeric thermoplastic material, such as thermoplastic polyurethane. The layers may have certain relationships among their hardness values. Finally, the golf ball exhibits certain physical properties, such as a certain moment of inertia.