Since I was curious about the relative densities, I looked it up and asked Google to convert to your archaic units. Water, at -30C, is around 60 lbs/ft³, so indeed the foam is denser.
I was _going_ to claim that water is denser still, way down deep in the ocean. But I thought I'd check it out first, and although I'm not well-educated enough to understand the important parts of phrases like "At 0 °C, at the limit of zero pressure, the compressibility is 5.1×10−10 Pa−1", I can understand this phrase: "The low compressibility of water means that even in the deep oceans at 4 km depth, where pressures are 40 MPa, there is only a 1.8% decrease in volume."
Oh, my bad. I misrecalled a detail from the featured article, thinking it had claimed that temperatures were very very low, so I picked the lowest temperature in that sidebar as a rough approximation. Actually, TFA says "near freezing", which certainly much closer to 4C than to -30C.
I was _going_ to claim that water is denser still, way down deep in the ocean. But I thought I'd check it out first, and although I'm not well-educated enough to understand the important parts of phrases like "At 0 °C, at the limit of zero pressure, the compressibility is 5.1×10−10 Pa−1", I can understand this phrase: "The low compressibility of water means that even in the deep oceans at 4 km depth, where pressures are 40 MPa, there is only a 1.8% decrease in volume."
http://en.wikipedia.org/wiki/Properties_of_water#Density_of_...