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 layersan 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.

Golf balls comprising a core having at least one layer and a cover having at least one layer are provided. At least one of the layers is made from a thermoplastic composition preferably comprising a borophene material. Mixtures of borophene material and polybutadiene rubbers or ethylene acid copolymers can be prepared. The borophene-containing compositions can be used to make a core layer having good strength and impact durability and it also should help provide the ball with high resiliency.

A golf ball for amateur golfers is endowed with an excellent flight when hit by the average golfer whose head speed is not that high and also has a good feel at impact that is soft and solid on full shots with all golf club numbers. The golf ball, which includes a core and a cover, has a compressive deformation A under 0.2 kgf to 5 kgf loading that is 0.21 mm or less and a compressive deformation B under 5 kgf to 30 kgf loading that is from 0.73 to 0.95 mm. Also, letting D be the compressive deformation of the ball under 10 kgf to 130 kgf loading and C be the compressive deformation of the ball under 5 kgf to 60 kgf loading, the ratio D/A is from 16.0 to 20.5 and the ratio D/C is from 1.80 to 1.90.

A golf ball for amateur golfers is endowed with both an excellent flight and a good, soft feel at impact when hit by the average golfer whose head speed is not very high. The golf ball, which includes a core and a cover, has a compressive deformation A when the ball is subjected to a final load of 5 kgf from an initial load state of 0.2 kgf that is 0.18 mm or less, a compressive deformation B when the ball is subjected to a final load of 15 kgf from an initial load state of 5 kgf that is from 0.30 to 0.38 mm, a compressive deformation C when the ball is subjected to a final load of 60 kgf from an initial load state of 5 kgf that is from 1.70 to 2.03 mm and a compressive deformation D when the ball is subjected to a final load of 130 kgf from an initial load state of 10 kgf that is from 3.10 to 3.80 mm.

A golf ball for amateur golfers is endowed with both an excellent flight and a good, solid feel at impact when hit by the average amateur golfer having a fast head speed. The golf ball, which includes a core and a cover, has a compressive deformation A when subjected to a final load of 5 kgf from an initial load of 0.2 kgf that is 0.18 mm or less, a compressive deformation B when subjected to a final load of 50 kgf from an initial load of 5 kgf that is from 0.85 to 1.16 mm and a compressive deformation C when subjected to a final load of 90 kgf from an initial load of 5 kgf that is from 1.90 to 2.25 mm.

A golf ball for amateur golfers is endowed with both an excellent flight and a good feel at impact that is soft and solid when hit by the average golfer whose head speed is not very high. The golf ball, which includes a core and a cover, has a compressive deformation A when subjected to a final load of 5 kg from an initial load of 0.2 kg that is 0.21 mm or less, a compressive deformation B when subjected to a final load of 30 kg from an initial load of 5 kg that is from 0.72 to 0.90 mm and a compressive deformation C when subjected to a final load of 60 kg from an initial load of 5 kg that is from 1.55 to 1.80 mm.

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.

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.