<p>Refractory metal high-entropy alloys (HEAs) with a body-centered cubic (bcc) structure are promising materials for hydrogen storage applications. The high hydrogen storage capacity of these refractory metal HEAs is not yet fully understood. It has been suggested that significant lattice distortions, caused by the differing atomic radii of the constituents in HEAs, blur the energy difference between hydrogen atoms absorbed in octahedral and tetrahedral interstitial sites. This may result in an enhanced hydrogen absorption capacity. However, directly characterizing these lattice distortions is challenging because they occur on an atomic scale and exhibit a stochastic nature. The magnitude of lattice distortion is typically expressed using the atomic misfit parameter, which is a phenomenological measure; however, it is not clear how accurately it describes the actual distortions present in the HEA lattice. In this study, we measured the hydrogen absorption capacity of a series of 20 refractory metal HEAs with various compositions. While we found a positive correlation between hydrogen absorption capacity and the atomic misfit parameter, our results suggest that the degree of local lattice strain is not the only factor influencing the hydrogen storage capacity of refractory metal HEAs. Additionally, the hydrogen absorption capacity is significantly affected by the valence electron concentration (VEC), which is negatively correlated with hydrogen absorption capacity. Furthermore, we employed positron annihilation spectroscopy (PAS) to evaluate the interstitial open volume in these refractory metal HEAs, each characterized by different values of the misfit parameter. The results indicate that the bulk positron lifetime increases as the misfit parameter rises, indicating that the magnitude of lattice distortions increases with the misfit parameter. This suggests that PAS can serve as a sensitive, though indirect, probe of the open volume at interstitial sites in HEAs.</p>