Abstract: A bumper system includes a bumper beam having top and bottom attachment features, such as apertures or concavities for attachment. A thermoformed polymeric energy absorber includes a base flange for engaging the face of the beam, protruding crush lobes for absorbing energy upon an impact, and top and bottom rear flanges. The top and bottom rear flanges include inwardly-facing protrusions defining a second dimension less than a first dimension of the beam's face, but the base flange is sufficiently resilient and flexible at desired locations and with desired force of flexures to provide tunable flexure points so the protrusions can be temporarily resiliently flexed apart to the first dimension for assembly and then upon release, the protrusions flex back to the second dimension engaging the attachment features to temporarily but positively retain the energy absorber on the beam.