A Short History of American Football Helmets - HubPages
Evolution of the Football Helmet
The Evolution of Football Helmets, by Jose Diaz
NFL Over the Years & Fun Facts - Custom Throwback Jerseys
Has American Football gain popularity in China? - Quora
Impact test comparisons of 20th and 21st century American football helmets in: Journal of Neurosurgery Volume 116 Issue 1 (2012) Journals
Digital Exhibits — Guilbeau Center for Public History
The History of The Football Helmet timeline
5 Pack - Entertainment Earth