In conjunction with colleagues in the chemical industry, we have developed and evaluated a new plastic prosthesis which we hope will supplant presently used materials for chest wall replacement. We have modified the basic chemical of a reactive resin routinely used in orthopaedic and dental work by the inclusion of a polypropylene mesh. The resultant material is thin enough to cut with scissors and yet supple enough to shape to fit the defects. It is hardened by exposure to UV light and has a practical cure time when exposed to normal light in the operating theatre. When set it is strong and rigid. The mechanical properties have been studied with the Flexural 3-point bend test and compared with the best of the presently available prostheses. The inert nature of the material was studied in a subcutaneous implant in 29 rats over 3 months. Histology has shown a lack of reactivity. The stability in vivo was studied using the material to replace portions of the chest wall in rabbits for up to 6 months. Subsequent histology and in-vitro testing have proved satisfactory. The ability of this material to withstand the dynamic stresses of the chest wall have been studied by its implantation into the chest wall of 3 minipigs for 6 months. The material looks promising and has proved more "user friendly" than existing prostheses for flat bone replacement. We hope to refine its production to allow its use in humans.