The particle size and shape of commercially available MgH2 have been characterised, together with those of ball milled MgH2. These parameters have then been compared with those obtained for the hydrogenated and dehydrogenated state. In addition, thermal conductivity measurements of each specimen have been made. The results show that significant changes occur upon dehydrogenation, which are contrary to expectation. These changes include an increase in average particle size of 28% post dehydrogenation for as received MgH2, rather than the theorised decrease, and an increase of approximately 300% post dehydrogenation in the ball milled MgH2 sample. The change in thermal conductivity between the two material states is also higher than expected with an average variation of 14% between the samples in the hydrogenated and dehydrogenated states. This investigation highlights the need for more thorough consideration of particle characteristics when simulating (de)hydrogenation reactions within powder beds in order to construct reliable simulations. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.