FOR THE repair of large hernias it is often found useful to use some foreign material to reinforce or replace the damaged tissues. Many substances have been advocated—metal plates and sutures,1 wire meshes2 and filigrees,3 bone plaques, skin4 and fascial implants.5 Many have been useful; some have been discarded soon after their introduction. This paper describes the investigation of a new material—polyvinyl formal sponge (Ivalon).* THE MATERIAL Polyvinyl (Ivalon) sponge is a polymer of polyvinyl alcohol with formaldehyde and is made commercially by foaming the substance during polymerization. Its possibilities in surgical techniques were first described by Grindlay and Clagett6 and Grindlay and Waugh7 who considered its use as a prosthesis following pneumonectomy and as a means of strengthening the wall of an abdominal aortic aneurysm. Unlike most other plastic materials being used in surgery, for example, polyethylene, nylon, Cellophane, and acrylic resin,