The First Plastic Football Helmet Often Broke on Impact - The Atlantic
Light helmet design's effectiveness pits company versus NFL, NFLPA and their testing - The Athletic
Football helmet with liquid padding may prevent concussions
Guardian Caps - Are the soft-shelled football helmet covers effective at limiting head injuries? - ESPN
A football helmet design that listens to physics – Mechanical Engineering
Wearing headgear for sport does not protect against concussion, Australian experts warn, Concussion in sport
How Effective Are Football Helmets at Preventing Brain Injuries?
Exactly How Dangerous Is Football?
Study links youth football to greater risk of later health problems - The Boston Globe
Guardian Caps', NFL's Most Recent Attempt At Preventing Head Injuries