In this work an analysis of the fracture behavior under impact of four epoxy resins was performed. The morphology of the fracture surfaces was analyzed by scanning electron microscopy and the topographic marks observed could be related to the thermal behavior of each epoxy system. The relevant properties that determine the thermal behavior were the thermal diffusivity, which was measured by using the open photoacoustic cell technique, and the glass transition temperature. As the thermal diffusivity of these materials is very low, and therefore also is their heat dissipation capacity, the impact test occurs under adiabatic conditions and a temperature increase occurs at the tip of the running cracks. Therefore, thermal blunting may occur at the crack tip and the energy absorption capacity of the resins is increased. The topographic marks observed at the fracture surface help to identify how efficient this mechanism is for each of the epoxy systems analyzed.