The N.F.L.'s Incredible Shrinking Pads - The New York Times
The Truth About the Safety Ratings That Sell Football Helmets - Bloomberg
The History of Football Helmets, Xenith
NFL at 100: Helmets go high tech in quest for player safety
Tua's helmet (description in post) : r/miamidolphins
Impact test comparisons of 20th and 21st century American football helmets in: Journal of Neurosurgery Volume 116 Issue 1 (2012) Journals
NFL at 100: Helmets go high tech in quest for player safety
Evolution of Football Equipment: Look at the Past, Present, and Future of Football Gear
Impact test comparisons of 20th and 21st century American football helmets in: Journal of Neurosurgery Volume 116 Issue 1 (2012) Journals
Vintage Football Protection Could Do More Harm Than Good
Old Leather Football Helmets More Efficient Than Modern Ones, Study Says
Shoulder Pads Slim Down in Faster, Sleeker N.F.L. - The New York Times
Helmets don't eliminate concussions. It's time for the NFL to ditch them, NFL
New Helmet Technology Aimed to Make Football and Other Sports Safer
PHOTOS: Check Out These Old School Leather Football Helmets in Color