I recently posted about an experiment with expanded polyurethane foam and I was asked in a forum about the relative density of it and the expanded polystyrene I had previously used.
1. GAGA-1 Expanded Polystyrene Container
Outside dimensions: 245mm cube
Inside dimensions: 150mm cube
Thus, volume is 0.01471 m^3 - 0.003375 m^3 = 0.011335 m^3
Which gives a density of 18,791.4 g/m^3
2. My experimental capsule using expanding polyurethane foam
Internal space: 100 mm x 65 mm x 35 mm
Thus, volume is 0.001272 m^3 - 2.275×10^-4 m^3 = 0.001045 m^3
Which gives a density of 23,923 g/m^3.
Thus the expanding polyurethane foam is about 25% heavier than expanded polystyrene for the same volume.
Various sources give the R-value give an approximate 2x increase in R-value of polyurethane over polystyrene. Thus for the same thickness it would be expected that the polyurethane is a better insulator at a slightly greater weight. And the insulation increase outweighs the extra weight (200% vs. 25%).