I don't see the advantage if you've got to lug around the same weight of shielding material . It's hardly surprising (to me, anyway ) that it takes a larger lump of foam to provide equivalent shielding to that of a smaller lump of solid.To make the best comparison, the researchers prepared each sample with the same areal density, with the test materials varying in volume but having the same weight.
I was wondering if it vould be so when I read yours above. What if externally covered by a thin plating of the same quality giving it some mechanical rigidity? Kind of those containers of various kind with a simple structure filled with some type of polyuretane..(?) Even lifeboats are /were? built like that.It's fragile and expensive.