Multi-layer golf ball

1. A golf ball comprising:

a solid core having an outer diameter of less than about 1.59 inches and comprising polybutadiene and a cis-to-trans catalyst such that, upon curing, the core has a first amount of trans-polybutadiene at an interior location and a second amount of trans-polybutadiene at a surface location, the first amount being at least about 6 percent less than the second amount;

an outer cover layer having a first material hardness and comprising a elastomer formed from a castable reactive liquid material; and

a casing disposed between the core and the cover layer, the casing comprising polyurea and having an outer diameter of between about 1.59 inches and about 1.64 inches and a second material hardness of between about 30 and about 70 Shore D;

wherein a ratio of the second material hardness to the first material hardness is greater than 1.5.

2. The golf ball of claim 1 , wherein the first material hardness is less than about 45 Shore D.

3. The golf ball of claim 2 , wherein the first material hardness is between about 25 and about 40 Shore D.

4. The golf ball of claim 1 , wherein the second material hardness is between about 50 and about 65 Shore D.

5. The golf ball of claim 1 , wherein at least one of the casing and the outer cover layer has a thickness of less than about 0.05 inches.

6. The golf ball of claim 5 , wherein at least one of the casing and the outer cover layer has a thickness of between about 0.02 inches and about 0.04 inches.

7. The golf ball of claim 1 , wherein the core has a vinyl polybutadiene isomer content of less than about 7 percent.

8. The golf ball of claim 1 , wherein the elastomer is a polyurethane composition comprising the reaction product of at least one polyisocyanate, a polyol, and at least one curing agent.

9. The golf ball of claim 1 , wherein the core has a first hardness at a point in the interior and a surface having a second hardness differing from the first hardness by greater than 10 percent.

10. The golf ball of claim 1 , wherein the core comprises a polybutadiene having a Mooney viscosity of between about 40 and about 80, a resilience index of at least about 50, or a dynamic stiffness of less than about 50,000 N/m at −50° C.

11. The golf ball of claim 1 , wherein the golf ball has a dimple coverage of greater than about 75 percent.

12. The golf ball of claim 1 , wherein the casing further comprises ionic copolymers of ethylene and an unsaturated monocarboxylic acid; vinyl resins; polyolefins; polyurethanes; polyamides; thermoplastic and thermoset resins; metallocenes; acrylic resins; or thermoplastic polyesters.

13. The golf ball of claim 1 , wherein the casing material hardness is between about 40 and about 70 Shore D and the outer cover layer material hardness is less than about 40 Shore D.

14. The golf ball of claim 1 , wherein at least one of the core, casing, and cover layer are cast, reaction injection molded, liquid injection molded, injection molded, or a mixture thereof.

15. A golf ball comprising:

a core having an outer diameter of less than about 1.59 inches and comprising a polybutadiene having a vinyl content of less than about 7 percent and comprising a cis-to-trans catalyst such that, upon curing, the core has a first amount of trans-polybutadiene at an interior location and a second amount of trans-polybutadiene at a surface location, the first amount being at least about 6 percent less than the second amount;

an outer cover layer having a first material hardness and formed from a polyurethane composition comprising the reaction product of at least one polyisocyanate, a polyol, and at least one curing agent; and

a casing disposed between the core and the cover layer, the casing comprising polyurea and having an outer diameter of between about 1.59 inches and about 1.64 inches and a second material hardness of between about 30 and about 70 Shore D;

wherein a ratio of the second material hardness to the first material hardness is greater than 1.5 and the golf ball has a moment of inertia of less than about 83 g-cm 2 .

16. The golf ball of claim 15 , wherein at least one of the casing and the outer cover layer has a thickness of less than about 0.05 inches.

17. The golf ball of claim 15 , wherein at least one of the casing and the outer cover layer has a thickness of between about 0.02 inches and about 0.04 inches.

18. The golf ball of claim 15 , wherein at least one of the casing or cover layer are cast, reaction injection molded, liquid injection molded, injection molded, or a mixture thereof.