Pores in cast, compacted or AM built material that shrink during HIP, can regrow if they are filled with argon and are subjected to high temperature. To better understand this, we present a study on a set of capsules that contain a huge 2 cm3 cavity (which in terms of volume is 109 bigger than a typical AM gas pore). These cavities were filled with argon by sealing them under 1 atm of 100% argon. Using HIP these cavities shrink to an approximate size of 0.01 cm3 resulting in a room temperature pressure of ~206 bars. Upon stepwise reheating the pressure increases, and for IN718 the cavity expands above 900 °C (pressure is here ~824 bar), while for 316L the cavity expands above 1000 °C (pressure is here ~895 bar). The temperature at which expansion occurs are not far from typical HIP conditions, which makes sense.