A thermoforming process capable of coining and flowing material is provided, such as for making a thermoformed energy absorber for self-attachment to a vehicle bumper beam. The energy absorber includes a thermoplastic sheet with first thickness shaped by a thermoforming process to include a base and lobes configured to absorb energy. The sheet further has integrally formed attachments with solid heads formed from material flowed from adjacent areas into the attachment during the thermoforming process. Many other structures can be formed, such as ringed ridges, thinned regions, snap-attachments, hooks, living hinges, bosses, and the like. The present invention further includes an apparatus and a method for accomplishing the above, such as a heater for heating the sheet, and a die for stretching and shaping the sheet, where heated material is flowed by opposing coining die components to form selectively-shaped 3D structures.