Funky-Looking Guardian Caps Rejected by NFL for Regulation Play, OK'd for Practice - Core77
EXPLAINER: NFL using helmet caps for player safety, research
Coverage of the NFL in Guardian Caps
NFL training camps: Guardian Cap players are wearing over helmets, why
NFL training camps: Guardian Cap players are wearing over helmets, why
Coach Prime, Buffs stage quite the show in snowy spring game
What's With Those Padded Caps NFL Players Are Wearing In Training Camp?
NFL's use of Guardian padded helmet caps in camp draws support and skepticism - The Athletic
NFL's use of Guardian padded helmet caps in camp draws support and skepticism - The Athletic