NFL's use of Guardian padded helmet caps in camp draws support and skepticism - The Athletic
NFL reports reduction in concussions among players who wore Guardian Caps in preseason - The Athletic
Soft Cover Football Helmet Add-ons
Ban on helmet covers sparks controversy
Florio PFT] The Guardian Cap apparently works. But if a player asks to wear it in a game, the league would say no. : r/nfl
EXPLAINER: NFL using helmet caps for player safety, research
NFL hopes to reduce head injuries with helmet experiment
Guardian Caps are the latest effort to address CTE, football concussion concerns
NFL mandates extra head protection for training camp
Football Guardian Cap draws mixed reviews from players, experts for safety effectiveness - The Daily Tar Heel
Colorado High School Activities Association bans use of helmet covers during games