1. The problem statement, all variables and given/known data This should be a pretty simple question but I can't find a straight answer in the literature. I want to simulate a 3D model of a metal foam by starting with an aluminum block and filling it with randomly placed spherical holes of constant volume. The foam should have a porosity of 20 ppi (pores per inch) and a volume ratio of 25% aluminum. How many pores should there be, and what are their sizes? 2. Relevant equations 20 pores per inch 25% aluminum, 75% void by volume 3. The attempt at a solution I'm not clear on precisely what "ppi" means. Does 20 ppi imply that a 1 inch cube of aluminum should contain 20^3 = 8000 pores? And that each pore should have a volume of 0.75/8000 = 0.00009375 in^3? This seems pretty obvious but I want to make sure before I proceed. Thank you for your help!