The Evolution of the Helmet
Sources -- AB says no football without old helmet - ESPN
The Bizarre History of the NFL's First Title Game
History of the Browns Helmet
13 NFL teams introduce alternate helmet looks for 2022 season
The History of the Football Helmet - Brain Injury Law Center
The First Plastic Football Helmet Often Broke on Impact - The Atlantic
Leatherhead to Radio-head: The Evolution of the Football Helmet
History of The Football Helmet - Atavus
The Football Helmet. Personal Selection, by Brandon Martin