A golf ball comprising a core comprising a highly-neutralized thermoplastic polymer formed from a copolymer of ethylene and an α,β-unsaturated carboxylic acid, a salt of an organic acid, and sufficient cation source to filly-neutralize the acid groups of the copolymer; an outer cover layer; and an inner cover layer disposed between the center and the outer cover layer, the inner cover layer having a specific gravity of 2.5 g/cc or greater; wherein the core has an outer diameter of 1.58 inches or greater and a coefficient of restitution of 0.805 or greater when measured at an incoming velocity of 125 ft/s.