The continuous development of sport technologies persistently demands advancements in protective headgear (helmets) to reduce the risk of head injuries. This paper introduces the development of a new helmet liner, developed through the performance study of two different design approaches. The first approach is to design liners through the study of biological structures. The second approach is to use topology optimization to design an array of compliant mechanisms. Bio-inspired designs are generated through the study of biological micro and macro hierarchical structures. An emphasis is given on biological mechanisms that serve similar concussion reducing functions as a helmet liner. Inspiration was draw from bone, animal infrastructures, and microscopic skeletal structures. Compliant mechanism-based designs start with the synthesis of two types of compliant mechanisms, designed through traditional density-based topology optimization techniques. The first mechanism operates with a positive Poisson’s ratio, where the Poisson’s ratio, in this case, is defined as the displacement ratio between the input and output ports of the compliant mechanism. The second mechanism operates with a negative Poisson’s ratio. These different mechanisms are assembled into three different liner arrangements. Liner implementation into the helmet is done by embedding the liner between an inner and outer polycarbonate shell, replacing the traditional expanded polypropylene foam liner of a standard sports helmet. Prospective liners are further developed through a series of ballistic impact tests to determine the final design and its rubber properties. The final liner is compared against an expanded polypropylene foam liner to appraise the protection capabilities of the proposed liner.