US Patent 7259191 Multi-layer golf ball with a foamed intermediate layer

A golf ball with relatively rigid inner core and soft intermediate layer is disclosed. The rigid inner core maintains the balls' high coefficient of restitution at high impact speeds, while the soft intermediate layer provides better feel for greenside play. The intermediate layer can be made from a highly neutralized polymer, which can be thermoset or thermoplastic. The highly neutralized polymer is foamed or otherwise has its specific gravity reduced. The intermediate layer can also be made from a castable reactive liquid polymer.