"ite, on applying energy such as steam, heat, or laser energy, provides an expanded article having increased void volume...http://www.google.es/patents/US5238621?utm_source=gb-gplus-sharePatente US5238621 - Method of controlling porosity in a composite article B???squeda avanzada de patentes N???mero de publicaci???nUS5238621 ATipo de publicaci???nConcesi???n N???mero de solicitudUS 07/906,274 Fech" . . . .