American football athletes are exposed to a high number of head impacts of varying severity throughout the course of regular play. The sport has a high rate of concussions, despite mitigating strategies, including protective helmets, when compared to other contact sports.

Current helmets commonly use elastomeric foams as the principal energy absorption mechanism to protect players from injury. However, these foams have limited performance ranges due to their mechanical properties. Therefore for better player protection, a novel material was required. Novel materials and structure combinations presented the ability to leverage material properties that had the potential to expand the performance range of a helmet liner. This study investigated a metamaterial based on stacked layers of the Miura Ori folding pattern, which offered both improved performance and ample scope for optimisation.

The Taguchi method was used to design a series of samples manufactured from thermoplastic polyurethane, tested using a series of validated impacts. Data from these impacts were used to refine the geometry, using statistical processes, such that measured accelerations and injury metrics were minimised. The metamaterial's final design was then tested as part of a helmet to establish the improvement in performance offered over the original foam liner.

The selected geometry reduced the risk of a player sustaining mild brain injuries while offering comparable protection against catastrophic injuries when impacted. This risk reduction not only reduces the number of injuries that could be expected over players’ careers but also has the potential to reduce the probability of players developing neurogenerative conditions later in their lives.