Golf ball having a hollow center

A golf ball comprising a hollow core, the golf ball comprising:

• a spherical inner core shell layer formed from a first thermoset rubber composition, the shell layer having an outer surface, an inner surface, and an inner diameter to define a hollow center;
• a thermoplastic outer core layer;
• a thermoplastic intermediate core layer disposed between the shell layer and the outer core layer;
• an inner cover layer disposed about the outer core layer, the inner cover comprising an ionomeric material and having a first hardness;
• and
• an outer cover layer disposed about the inner cover layer, the outer cover comprising a polyurea or a polyurethane and having a second hardness less than the first;
• wherein the hollow center has a diameter of about 0.15 to 1.1 inches, the shell layer has a surface hardness greater than an inner surface hardness by about 3 to 25 Shore C to define a first hardness gradient, and the thermoplastic outer core layer or the thermoplastic intermediate core layer has a second hardness gradient.

A golf ball comprising a hollow core, the golf ball comprising:

• a spherical inner core shell layer formed from a first thermoset rubber composition, the shell layer having an outer surface, an inner surface, and an inner diameter to define a hollow center;
• a thermoplastic outer core layer;
• a thermoset intermediate core layer disposed between the shell layer and the outer core layer, the intermediate core layer comprising a second thermoset rubber composition different from the first;
• an inner cover layer disposed about the outer core layer, the inner cover comprising an ionomeric material and having a hardness greater than about 60 Shore D;
• and
• an outer cover layer disposed about the inner cover layer, the outer cover comprising a polyurea or a polyurethane and having a hardness less than about 60 Shore D;
• wherein the hollow center has a diameter of about 0.51 to 1.1 inches, the shell layer has a surface hardness greater than an inner surface hardness by about 3 to 25 Shore C to define a first hardness gradient, the thermoplastic outer core layer has a second hardness gradient, and the thermoset intermediate core layer has a third hardness gradient different from the first or second hardness gradients.