Provided in an energy absorber (1) for bumpers (2, 3) of motor vehicles are stiffening elements (5), which have free-standing front sides (6) facing away from a rear mounting structure (4). The stiffening elements (5) have in the longitudinal direction a lateral center-to-center distance from one another that corresponds to the standard dimensions of a human leg. Side faces of the stiffening elements (5) which face one another are designed such that, in the event of collision with a leg, the stiffening elements (5) are deformable independently of one another, and in the event of collision with an object larger than a leg, the stiffening elements (5) engage one another at their side faces in a manner hindering deformation with an abrupt increase in the stiffness of the energy absorber (1). By this means, braking with a relatively low deceleration is achieved in a collision with the leg, whereas the energy absorber (1) is adequately stiff in a collision with a larger object.