Patent 7125343 was granted and assigned to Bridgestone on October, 2006 by the United States Patent and Trademark Office.
A recess portion is provided on a rear face of a head main body. A resin layer is bonded between ribs, of an innermost face. After an element assembly of the resin layer, an element assembly of the FRP body and a balloon are inserted into the recess portion, the iron golf club head is mounted in a mold, and a gas such as air is supplied into the balloon through an air opening inserted into an opening.