| abstract |
A golf ball 2 includes a core 4 and a cover 6. The core 4 includes a center 8 and an envelope layer 10 each of which is formed by a rubber composition being crosslinked. At least one of the rubber compositions of the center 8 and the envelope layer 10 includes a base rubber (a), a co-crosslinking agent (b), a crosslinking initiator (c), and an acid and/or a salt (d). The co-crosslinking agent (b) is: (b1) an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms; or (b2) a metal salt of an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms. A hardness H (Ie) at an innermost portion of the envelope layer 10 is greater than a hardness H(Sc) at an outermost portion of the center 8. A hardness Ho of the cover 6 is greater than a hardness Hs at a surface of the core 4. |