The clinical application of silicone rubber is based on a high degree of tolerance by the body and the lack of foreign-body reaction. This material has been used in plastic correction of facial bony defects and nasal deformities, soft tissue augmentation, tubes and valves for the relief of hydrocephalus, heart valve prostheses, and in repair of meningoceles and defects of the dura mater. Silicone rubber has been considered an ideal substitute for soft tissues.1It appears to be inert and nonirritating, to cause minimal fibrous tissue formation, and no foreign-body reaction. In this experiment Dacron, calendered with Silastic of 0.007 in. thickness—a fine, nonporous, resistant fabric—was studied, first to observe its fate as a partial pericardial prosthesis, and second to show the resultant neighboring tissue reaction in surgically produced pericardial defects. In a previous experiment,2the lack of peritoneal adhesion to a tubular drain and the occasional