Abstract A composite structural buffer has been designed to reduce the peak impact load of the projectile during high-speed water entry. The Expanded Polystyrene (EPS), Rigid Polyurethane (PU) and ALPORAS® aluminium foams are used to be the load-reducing material for the buffer, respectively. The constitutive model for the material has been validated by comparing the numerical results with the compressive tests data. Six deformation and failure modes: Local Failure (LF), Warping Deformation/Failure (WD/WF), Wedging-In Failure (WIF), Euler Failure (EF), Inversion and Curling (IC), Complete Disintegration (CD) are found in the nose cap during water entry at constant vertical velocity. Among these modes, the wedging force in WIF mode is the dominant cause of the severe damage of the nose cap. The results show that the material performance of the damper has a more significant influence on the CD mode time than the length of nose cap, the beginning time of WIF mode and the duration of WIF mode. Moreover, the ALPORAS® aluminium foam has the best load-reducing performance (highest load-reducing ratio up to 75.3%) among the three foam materials. This paper provides an engineering reference for the design of buffer applied in high-speed water entry.