We analyzed the effect of placing an energy-dissipation barrier under a vehicle to improve its blast resistance. We developed a simplified first-principle model to estimate the momentum transfer from soil to the vehicle during the impact of the fast moving soil with the underbody. The model considers a continuous collision of soil stream with the underbody; it accounts for the foam yield stress resisting the underbody motion and the stroke-reduction penalty that results from the finite foam compression distance. Our results indicate that in terms of reduction of momentum transferred to the vehicle from the fast moving soil, an upper bound on improvement of the vehicle blast resistance due to placing an energy-dissipative underbody barrier is on the order of 5% to 8%.