Evolution of Football Helmets – 2nd Skull, Inc.
3D printing's breakout season: A look at Riddell's Precision Diamond helmet - TCT Magazine
Helmet Innovation: More and Better Choices, Fewer Concussions
A Simple Guide to Motorcycle Helmet Ratings
Can a Better Football Helmet Save Your Kid's Brain? - Washingtonian
The Zero1 Flexible Football Helmet May Save Players' Brains
Researchers test old-style leather helmets vs. modern ones and found leather performed as well, better in some aspects. Conclusion: Football helmets need to be softer. : r/nfl
History of the NFL Helmet
Helmets don't eliminate concussions. It's time for the NFL to ditch them, NFL
Football helmets have improved but are far from 'concussion proof' – Orange County Register
Better helmets, sensored mouth guards part of effort to make football safer
Testing football helmets, 1912 - Rare Historical Photos
Football Friday Nights: The Product Evolution of the Helmet
New Helmet Technology Aimed to Make Football and Other Sports Safer
Large Bubble Helmets Are Guardian Caps, NFL's New Safety Measure