This proposal aims to use NIMROD to glean information on the mechanisms of pore filling and to obtain a quantitative absolute value for the density of supercritical hydrogen (H2) adsorbed into nanoporous hydrogen storage materials at cryogenic temperatures and high pressures.We will collect spectra from three well-characterised carbide-derived carbon materials having systematically increasing pore diameters at 77 K to obtain a direct measure of the densities of H2 adsorbed as a function of in-situ gas dosing pressure (up to 50 bar). In addition, we will use H/D contrast matching to obtain information on the distribution of the condensed phase. Finally, to ascertain whether adsorptive H2 densification is primarily a result of confinement or whether surface interactions play a significant role, the density of the hydrogen in a very high uptake MOF material will be measured.