a golf ball comprising : a core ; a casing layer surrounding the core ; and a cover layer surrounding the casing layer and being formed from a cover composition that is produced by a reaction of a prepolymer and a chain extender , wherein the prepolymer is formed from the reaction product of : an isocyanate comprising an allophanate and having an average nco functionality in the range of 1 . 9 to 2 . 8 and a polyol - containing component or an amine - containing component or a blend thereof ; and wherein the chain - extender is selected from the group consisting of amine - terminated chain - extenders , hydroxyl - terminated chain - extenders , and mixtures thereof . the ica may comprise a reaction product of hexamethylene diisocyanate , at least one monoalcohol , and a bismuth - containing catalyst . the ica may have an average equivalent weight of from about 200 to about 350 ; and the prepolymer may have an average equivalent weight of from about 420 to about 840 . the cover has a thickness of at least about 0 . 010 in . and a flexural modulus of about 10 , 000 psi or greater .