the present invention describes a die to manufacture pieces of plastic materials , molded by injection , projection or blowing processes that does not need end finishing during its construction , and that does not need to employ additional demolding agents during its whole useful life to release the objects molded . said die is specially useful to obtain pieces of plastic materials that must be painted or must be dealt superficially with the purpose of being employed in various industries , such as the automobile industry , electro - domestic accessories manufacturing , communications , computers , or decoration , etc . this die is also specially useful to obtain pieces that must be adhered in an efficient and substantially permanent way to others as are the soles for the industrial manufacturing of shoes and of sports shoes . there are also described the methods to manufacture or repair the dies , together with a process to prepare the silicon rubber by addition , herein referred to as srba , which is modified to be useful in said methods .