from 2 minutes to 10 hours in order to bond the metal the resulting product is a metal foam having an open cell structure characterized by a plurality of interconnected voids surrounded by a web of the metal the metal foam may have any desired configuration based on the configuration needed for the particular filtration process foam porosity is typically reported as an inverse length based on the theoretical average number of pores per distance assuming common struts there between foam porosity is therefore reported as pores per inch ppi or pores per mm ppm for example a foam reported as 3 93 ppm 100 ppi would have an average diameter of 0 254 mm 0 01 inches for the purposes of the present invention it is preferable that the foam have a porosity of 0 119 ppm 3 ppi to 3 93 ppm 100 ppi foam porosity is also reported as percent theoretical density theoretical density is calculated based on the density of a solid material with the same composition without voids which also corresponds to a crystallographic unit cell density as well known in the art percent theoretical density is the ratio of the actual density to the theoretical density for example for a material with a theoretical density of 8 grams cc and an actual density of 7 2 grams cc the percent theoretical density would be 80 for the purposes of the.