EXPLAINER: NFL using helmet caps for player safety, research - The San Diego Union-Tribune
NFL hopes to reduce head injuries with helmet experiment
Researchers test old-style leather helmets vs. modern ones and found leather performed as well, better in some aspects. Conclusion: Football helmets need to be softer. : r/nfl
NFL using helmet caps for player safety, research – News-Herald
Guardian Caps - Are the soft-shelled football helmet covers effective at limiting head injuries? - ESPN
NFL's use of Guardian padded helmet caps in camp draws support and skepticism - The Athletic
NFL players experiment with 'Guardian Caps' to protect heads
Guardian Caps Guardian Sports
EXPLAINER: NFL using helmet caps for player safety, research