Packed bed reactors using metal hydride are attracting a lot of attention as potential future hydrogen storage systems, actuators, etc. However, their low effective thermal conductivities lead to low performance. In this study, carbon fiber brush with high thermal conductivity was installed in a reactor to improve the effective thermal conductivity. We found that the carbon fiber brush at 1.0 vol% reduced the reaction time by 30%. A two-dimensional mathematical model describing the heat and mass transfer was developed to predict the thermal performance. Expansion of particles due to absorption is also considered in this model. The model was compared with the experimental results, and it predicted the time variations of the averaged reacted fraction and local reactor temperature very well. The model suggests that heat transfer rather than mass transfer controls the overall reaction.