Armor on the Field: The NFL's Headlong Race to Build the
New Player-Specific Football Helmets Could Reduce Head Trauma
Puffy, spongy Guardian Caps could help curb NFL head injuries
Football helmets don't protect against concussion — and we're not
PDF) External Foam Layers to Football Helmets Reduce Head Impact
Will head injuries kill football?
Design and Virtual Testing of American Football Helmets–A Review
More padding the issue of concussions and better helmets
Applied Sciences, Free Full-Text