Golf balls including cores formed from polybutadiene reaction products having a percent change in dynamic stiffness from 0° C. to −50° C. of less than 130 percent where the reaction products include a resilient polymer component, a crosslinking material, a cis-to-trans catalyst, and a free radical source. The golf balls may be formed with polyurethane covers, covers formed from castable reactive liquid materials, among other materials. The golf balls may also include an intermediate layer.