Multi-layered golf balls having at least one layer made of a foamed silicone composition are provided. Multi-layered golf balls having at least one layer made of non-foamed silicone elastomer composition also are provided. For example, three-piece, four-piece, and five-piece golf balls containing different core and cover structures can be made. The foamed silicones have good thermal stability and durability without sacrificing resiliency. The non-foamed silicone elastomers have high elongation, tensile strength, chemical/fluid-resistance, and weatherability properties. These compositions can be used to form any layer, for example, core, intermediate, or cover, in the golf ball.

Multi-layered golf balls having at least one layer made from silicone (polysiloxane) elastomers; silicone (polysiloxane) elastomer/polyurethane blends; polycarbonate-polysiloxane blends and copolymers; and polycarbonate-polysiloxane/polyurethane blends are provided. For example, three-piece, four-piece, and five-piece golf balls containing different core and cover structures can be made. The polysiloxane compositions have good thermal stability and durability without sacrificing resiliency. The polysiloxane compositions also have high elongation, tensile strength, chemical/fluid-resistance, and weatherability properties. These compositions can be used to form any layer, for example, core, intermediate, or cover, in the golf ball.

Golf balls having cores with increased hardness gradients are provided. The cores have an increased “positive” hardness gradient (or a “hard-to-soft” hardness) where the outer surface of the core is harder than the center. The increased positive hardness gradient can be achieved by introducing a water-releasing agent into the core rubber formulation during the curing process. The resulting golf balls have reduced spin and sufficient impact durability.

Golf balls having cores with increased hardness gradients are provided. The cores have an increased “positive” hardness gradient (or a “hard-to-soft” hardness) where the outer surface of the core is harder than the center. The increased positive hardness gradient can be achieved by introducing a water-releasing agent into the core rubber formulation during the curing process. The resulting golf balls have reduced spin and sufficient impact durability.

Golf balls having cores with increased hardness gradients are provided. The cores have an increased “positive” hardness gradient (or a “hard-to-soft” hardness) where the outer surface of the core is harder than the center. The increased positive hardness gradient can be achieved by introducing a water-releasing agent into the core rubber formulation during the curing process. The resulting golf balls have reduced spin and sufficient impact durability.

A golf ball for amateur golfers is endowed with an excellent flight and a good feel at impact that is soft yet solid when hit by a golfer whose head speed is not very high. The ball, which includes a core and a cover, has a compressive deformation B when subjected to a final load of 30 kgf from an initial load state of 5 kgf that is from 0.72 to 0.97 mm and a compressive deformation C when subjected to a final load of 60 kgf from an initial load state of 5 kgf that is from 1.55 to 1.85 mm. In addition, the core has a hardness profile which satisfies specific conditions.

In a golf ball having a core composed of one or more layer, the outermost layer of the core is formed of a rubber composition containing a base rubber and an α,β-unsaturated metal carboxylate, an envelope layer directly encasing the core is formed of a resin composition containing a thermoplastic resin having a structure that includes α,β-ethylenically unsaturated carboxylic acid copolymerization units, and a surface of the core outermost layer and the envelope layer adjoin each other through an intervening oxazoline group-containing substance. The golf ball has improved adhesion between the rubber-based core and the cover layer that directly encases the core and is formed of an ionomer resin or other α,β-ethylenically unsaturated carboxylic acid copolymer-containing resin material.

In a multi-piece solid golf ball having a core, an envelope layer, an intermediate layer and a cover, the envelope layer is formed into two layers—an inner envelope layer and an outer envelope layer. The inner envelope layer-encased sphere, outer envelope layer-encased sphere, intermediate layer-encased sphere and ball have respective surface hardness that satisfy a specific relationship. The inner envelope layer or outer envelope layer is formed primarily of one or more elastomer, and further the core has a particular hardness profile. This ball has an excellent flight when struck by golfers whose head speeds are not that fast and has a good, soft feel at impact, thus making it highly suitable for amateur golfers,

In a golf ball having a core, an intermediate layer and a cover, the core is formed primarily of a base rubber and has a diameter set in a specific range, and the intermediate layer and cover are each formed of resin materials. The core has an internal hardness such that, regarding the hardness at the core center, the hardnesses at positions located at 2 mm intervals from the core center outward up to 16 mm and the core surface hardness, the hardness differences therebetween are set within a specific range. The ball surface hardness is set so as to be higher than the surface hardness of the intermediate layer-encased sphere. This ball achieves a satisfactory distance on full shots not only with a driver, but also with a long iron or a middle iron, in addition to which it has an excellent durability to repeated impact.

In a multi-piece solid golf ball having a core, an envelope layer, an intermediate layer and a cover, the intermediate layer is formed into two layers—an inner layer and an outer layer. The surface hardness of the envelope layer-encased sphere, the surface hardness of the inner intermediate layer-encased sphere, the surface hardness of the outer intermediate layer-encased sphere and the surface hardness of the ball together satisfy a specific relationship. This ball has an excellent flight when struck by golfers whose head speeds are not that fast and has a soft yet good feel at impact, thus making it highly suitable for amateur golfers.