In the ever-increasing push to decrease the total weight of the modern soldier, helmets have been at the forefront. From European medieval knight helmets ranging up to 7 lbs to most modern-day ballistic helmets that weigh less than 3 lbs, the name of the game has been weight reduction. There is one major problem though, "The reduction in the helmet weight tends to result in a large backface deformation (BFD), which can lead to head injuries known as behind helmet blunt trauma (BHBT) for soldiers in battleﬁelds" (Li 2015).
While there have been a number of amazing breakthroughs in fiber technology allowing for lighter and lighter ballistic helmets that meet the National Institute Of Justice (NIJ) Resistance To Penetration (RTP) IIIA standards, they typically fail to meet safe BFD standards.
Following the study sighted above, stand-off distance (gap between helmet and head), helmet thickness, and of course impact direction play pivotal roles in the amount of stress that is transmitted to the brain. Utilizing the model and chart below we see that even a 2-mm thicker shell, about the thickness of a single layer of Kevlar fiber results in a 6.2% decrease maximum von Mises stress in the compact cranial bone.
That 2-mm thicker helmet or more means extra weight, but significantly better levels of protection as well. By extra weight, we also mean less than 1/2-3/4 of a single pound to gain 2-4 mm's of extra thickness.
This is why in the design of the Hard Head Veterans ATE ballistic helmet we opted for better protection than slight weight savings.
If you would like to learn more about blunt trauma induced by ballistic impact and the numerous other factors that play key roles we would strongly suggest visiting the cited research below!
Li, Xiaogai & Gao, X.-L & Kleiven, Svein. (2015). Behind helmet blunt trauma induced by ballistic impact: A computational model. International Journal of Impact Engineering. 91. . 10.1016/j.ijimpeng.2015.12.010. • Developed a finite element model for evaluating behind helmet blunt trauma (BHBT) arising from helmet's back face deformation under ballistic impact