A lost positive pattern comprising an open-pored plastics substrate containing pores with an average width of from one to three millimeters is used, in which, after a negative pattern has been made, the voids which it, as a core, contains are filled with metal by casting and the negative pattern is removed....http://www.google.es/patents/US5042560?utm_source=gb-gplus-sharePatente US5042560 - Method of producing open-celled metal structures
