I have a polymer processing teacher that has decided to give us a final exam with a bunch of questions we have not covered the entire semester. I've figured out most of them but this particular one has me stumped. I am given the dimensions for a part made of a known material and need to calculate the density required for a foam insert to be able to keep a certain weight afloat. I know I need to calculate the weight of the part and add that to the total weight being supported but am not sure how to calculate the necessary foam density. Can anyone provide links to some resources that may be useful? My googling attempts haven't turned up anything so far.