A golf ball is composed of at least a pair of adjacent concentric solid layers or three adjacent concentric solid layers. In the former case, the outer solid layer is composed of a matrix and non-metallic high-hardness grains having hardness higher than that of the matrix which has a Shore D range of...http://www.google.es/patents/US5961401?utm_source=gb-gplus-sharePatente US5961401 - Golf balls
