G Warwick, Aciturri installs LH2 tank into fuselage, Tech take, Aviation Week & Space Technology, 26 September-9 October 2022, p 54

In Europe, Aciturri in Spain is leading the Overleaf project to develop a liquid hydrogen tank integrated into the aircraft fuselage. Whereas the gravimetric index (= fuel mass/full fuel system and tank) is 100% for jet fuel, that for liquid hydrogen is barely 20% rather than the required 35%. The proposed system aims at a GI of 60%, with a maximum pressure of 90 psi instead of the usual 150 psi.