A football helmet prototype that reduces linear and rotational acceleration with the addition of an outer shell

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Amid the public health controversy surrounding American football, a helmet that can reduce linear and rotational acceleration has the potential to decrease forces transmitted to the brain. The authors hypothesized that a football helmet with an outer shell would reduce both linear and rotational acceleration. The authors’ objectives were to 1) determine an optimal material for a shock-absorbing outer shell and 2) examine the ability of an outer shell to reduce linear and/or rotational acceleration.


A laboratory-based investigation was undertaken using an extra-large Riddell Revolution football helmet. Two materials (Dow Corning Dilatant Compound and Sorbothane) were selected for their non-Newtonian properties (changes in viscosity with shear stress) to develop an outer shell. External pads were attached securely to the helmet at 3 locations: the front boss, the side, and the back. The helmet was impacted 5 times per location at 6 m/sec with pneumatic ram testing. Two-sample t-tests were used to evaluate linear/rotational acceleration differences between a helmet with and a helmet without the outer shell.


Sorbothane was superior to the Dow Corning compound in force reduction and recovered from impact without permanent deformation. Of 5 different grades, 70-duro (a unit of hardness measured with a durometer) Sorbothane was found to have the greatest energy dissipation and stiffness, and it was chosen as the optimal outer-shell material. The helmet prototype with the outer shell reduced linear acceleration by 5.8% (from 75.4g to 71.1g; p < 0.001) and 10.8% (from 89.5g to 79.8g; p = 0.033) at the side and front boss locations, respectively, and reduced rotational acceleration by 49.8% (from 9312.8 rad/sec2 to 4671.7 rad/sed2; p < 0.001) at the front boss location.


Sorbothane (70 duro) was chosen as the optimal outer-shell material. In the outer-shell prototype helmet, the results demonstrated a 5%–10% reduction in linear acceleration at the side and front boss locations, and a 50% reduction in rotational acceleration at the front boss location. Given the paucity of publicly reported helmet-design literature and the importance of rotational acceleration in head injuries, the substantial reduction seen in rotational acceleration with this outer-shell prototype holds the potential for future helmet-design improvements.

ABBREVIATIONS EDP = energy-dissipating pod; NCAA = National Collegiate Athletic Association; SRC = sport-related concussion.

Article Information

Correspondence Scott L. Zuckerman: Vanderbilt University School of Medicine, Nashville, TN. scott.zuckerman@vanderbilt.edu.

INCLUDE WHEN CITING Published online June 29, 2018; DOI: 10.3171/2018.1.JNS172733.

Disclosures Dr. Solomon receives consulting fees from the Nashville Predators (National Hockey League), the Tennessee Titans (National Football League [NFL]), University of Tennessee Athletics, Tennessee Tech Athletics, and the NFL; fees are paid to his institution. In addition, he is a consultant to the NFL Department of Health and Safety.

© AANS, except where prohibited by US copyright law.



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    Riddell Revolution helmet. Figure is available in color online only.

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    Shell with EDPs at the front boss (A), side (B), and back (C) of the helmet. Figure is available in color online only.

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    Forces measured in drop testing on the Dow Corning 3179 and Sorbothane non-Newtonian materials. Asterisk indicates statistical significance. Figure is available in color online only.

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    A: Force-versus-displacement curves determined via tensile testing for the various Sorbothane grades. The testing apparatus had a displacement limit of 50 mm, and the 70-duro sample was the only one that experienced failure within that displacement limit, as displayed by the drop-off in the 70-duro curve. B: Drop-testing results validated the use of 70-duro Sorbothane. Asterisk indicates significant difference between control and 50-duro Sorbothane; double asterisks indicate significant difference between control and 70-duro Sorbothane. Figure is available in color online only.

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    A: Linear acceleration experienced by the Hybrid III headform with the control and experimental helmets after 6 m/sec linear impacts at the 3 given locations. B: Rotational acceleration experienced by the Hybrid III headform with the control and experimental helmets after 6 m/sec linear impacts at the 3 given locations. G’s, acceleration (g); asterisk indicates statistical significance. Figure is available in color online only.


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