Helmets for sports applications are generally made up of three main components: a solid outer shell (to bear the impact load), a foam liner (to dissipate the impact energy) and assorted straps and pads. This approach relies on the properties of different materials that are glued and sued each other; nevertheless, the resulting product is not effortlessly recyclable. In this work, an innovative process based on the topology optimization approach and the graded foaming technology is described. The optimum mass distribution, designed to comply with the impact load, is achieved by applying nontrivial saturation conditions to a single thermoplastic recyclable polymer. The complex blowing agent concentration profile generated in the polymer results, after the gas release, in a product characterized by density and porosity gradients within its volume. Here, the external layer is dense and stiff whereas, moving to the inner parts, the material gradually turns light and soft.