© 2014, International Sports Engineering Association. Recent studies suggest that concussion may be associated with long-term neurological sequelae. Both linear impact and rotational acceleration have been identified as contributors to concussion and traumatic brain injury (TBI). Modern football helmets are designed according to the National Operating Committee on Standards for Athletic Equipment (NOCSAE) standard for protection from linear impact, without consideration of protection from rotational injury. A multidisciplinary team was assembled with expertise in brain injury, computational modeling, and materials engineering to design, fabricate and impact test a novel helmet padding system. A rotational fixture with magnesium headform and linear impactor was constructed using a rotary encoder to enable measurement of z axis rotational angle, velocity and acceleration. Helmet padding material designs were evaluated using finite element (FE) computational modeling, fabricated to specification and then impact tested. Models from two different manufacturers were retrofit with prototype pads and then compared with unmodified versions for attenuation of rotational acceleration. The helmets were then tested using a standard NOCSAE drop apparatus and headform for linear acceleration performance. Large-size Riddell Revolution and Schutt ION4D helmets retrofit with prototype padding demonstrated 21.6 and 33.6 % decreased peak z axis rotational acceleration following a 3.2 m/s side impact compared with their respective unmodified commercial models (717.7 vs. 914.0 rad/s2 and 768.4 vs. 1,158.6 rad/s2, p < 0.0001, respectively). The improved performance effect appeared consistent over at least 50 impacts without evidence of early material degradation or helmet damage. Compared with unmodified versions, drop test performance for hybridized helmets, measured by Peak G and severity index (SI), were comparable for most, but were worse for rear (Riddell Revolution) and side (Schutt ION4D) impact conditions. Rotational acceleration from side impacts may be attenuated by directed helmet design while maintaining acceptable linear impact performance. Future work will focus on optimization and durability testing of prototype padding for larger impacts.