Temperature Effects on the Impact Attenuation Performance of American Football Helmets and Padding Materials.

While American football games are played across a wide range of temperatures, current helmet rating protocols assess performance primarily at room temperature. This study evaluates how temperature influences impact attenuation performance of American football helmets and their padding systems. Six top-ranked NFL helmet models and their padding units were tested at four controlled temperatures (- 10, 5, 23, and 38 °C). Padding units were evaluated using drop tests (4.9 kg, 2.4 m/s) to measure peak acceleration, transmitted force, strain, and impact duration. Helmets were tested using a linear impactor (15.6 kg, 5.5 m/s) with a Hybrid III headform instrumented for measuring head peak linear accelerations (PLA) and angular velocities (PAV). Head injury criterion (HIC) and DAMAGE metrics were also calculated. Colder conditions (- 10, 5 °C), compared to room temperature (23 °C), stiffened padding responses, significantly increasing peak acceleration and transmitted force by up to 307% and 331%, respectively, while reducing strain and impact duration in drop testing. Similarly, helmet tests showed significant increases up to 56%, 44%, 86%, and 23% in PLA, PAV, HIC, and DAMAGE, respectively, compared to 23 °C. Warm conditions (38 °C) softened padding materials, producing significantly higher strain and impact durations by up to 38% and 56%, respectively, while helmet-level responses showed no significant change across head kinematic or injury metrics, compared to 23 °C. These findings demonstrate that temperature can influence impact attenuation performance of helmets. Incorporating more comprehensive temperature-dependent evaluation into helmet design and rating protocols is essential, ensuring consistent protection across diverse environmental conditions.