The HP allotropes of Hafnia, HfO2, have attracted attention for decades because of their potential for applications ranging from hard oxide coatings to resistive-switch memories. HP experiments have reported bulk moduli up to 340 GPa for the recoverable ortho-II phase using XRD at 300K; however, this approach can lead to big uncertainties, especially for highly incompressible materials; furthermore, direct measurements of the material’s hardness are scarce, and no recovery of the HP ortho-I phase was reported. Here, we propose to use the setup at ID06-LVP to combine in situ structural and ultrasonic interferometry measurements to provide the first reliable estimation of the adiabatic bulk and shear moduli of HfO2 at HP-HT conditions. This information will be essential to assess the capabilities and opportunities for its wide-ranging applications. Furthermore, we will optimize the synthesis and recovery P-T pathways, still lacking for the ortho-I phase.