Abstract The ballistic performance of ultra-high molecular weight polyethylene (UHMWPE) laminated plates and UHMWPE encapsulated aluminum structures were numerically characterized. Full three-dimensional continuum model for each type of target was built, and the UHMWPE was simulated using a sub-laminate approach with a composite material model. Simulation results were compared with existing experimental measurements, with good agreement achieved both on final deformation morphology and ballistic data. Underlying penetration mechanisms of laminated plate were then explored, and the effect of interface strength was quantified. The ballistic improvement of UHMWPE encapsulated aluminum structures was mainly attributed to the stretching of lateral swathing laminates. However, the benefit of encapsulation decreased as the initial impact velocity or lateral dimensions of encapsulated structure were increased. These findings are helpful for designing lightweight UHMWPE composite structures with superior ballistic resistance.