Liquid hydrogen has a density comparable to styrofoam.

Factual claim about physical properties, judged as of 2021-01-27. Compare the standard density of liquid hydrogen at its normal boiling point with typical densities of styrofoam (expanded or extruded polystyrene foam), as given in reference sources. TRUE: the density of liquid hydrogen falls within the typical published range for styrofoam. MOSTLY TRUE: it lies just outside that range, within about a factor of 1.5 of the range's nearest edge, so 'styrofoam-level' is a fair rough description. MIXED: it is within about a factor of 2 to 3. FALSE: it differs from typical styrofoam density by about an order of magnitude or more.

Set before the research began.

1. E1 Density - Sciencemadness Wiki Sciencemadness Wiki · 20 August 2025

   “Hydrogen (liquid) | 70 | At –255 °C”

2. E2 Density - Sciencemadness Wiki Sciencemadness Wiki · 20 August 2025

   “Styrofoam | 75 | Average type of styrofoam”

3. E3 Process Data set: Extruded Polystyrene (XPS) Foam Insulation with halogen free blowing agent (en) ÖKOBAUDAT (German federal sustainable building database) · 3 December 2019

   “Extruded polystyrene foam (XPS) is a thermoplastic insulation foam produced according to /EN 13164/ Building insulation, /EN 14307/ Equipment insulation, /EN 14934/ Civil engineering and available in board shape with a density range from 20 to 50 kg/m3.”

E1 lists liquid hydrogen at 70 kg/m3 at –255 °C, close to its normal boiling point. E2, from the same reference table, lists "average type of styrofoam" at 75 kg/m3. E3 gives a range of 20–50 kg/m3 for extruded polystyrene boards. Taken together, the published styrofoam values run from about 20 to 75 kg/m3, so liquid hydrogen falls within that range. Even against E3's range alone, 70 kg/m3 is only about 1.4 times the 50 kg/m3 upper edge, which makes "styrofoam-level" a fair description.