Ban on helmet covers sparks controversy
NFL training camps: Guardian Cap players are wearing over helmets, why
Why Marine City Cardinal Mooney football spent $35,000 on new helmets
Everything you need to know about the NFL's helmet guidelines and restrictions - Canal Street Chronicles
Guardian Caps - Are the soft-shelled football helmet covers effective at limiting head injuries? - ESPN
EXPLAINER: NFL using helmet caps for player safety, research
NFL executive hints that Guardian Caps could eventually be worn in games, along with position-specific helmets
Packers share thoughts on wearing Guardian Caps at camp
Chicago Bears: Why players are wearing padded helmets
Leatherhead to Radio-head: The Evolution of the Football Helmet, Arts & Culture
If a player wanted to wear a Guardian Cap during a game, the league would prohibit it - NBC Sports
EXPLAINER: NFL using helmet caps for player safety, research