EXPLAINER: NFL using helmet caps for player safety, research - The San Diego Union-Tribune
NFL's use of Guardian padded helmet caps in camp draws support and skepticism - The Athletic
If a player wanted to wear a Guardian Cap during a game, the league would prohibit it - NBC Sports
NFL players wear Guardian Caps to reduce head trauma during training camp
What are those funny-looking soft caps on NFL helmets during camp?, Sports
Morse says 'Halo' helmets making a difference
What are NFL players wearing on their helmets at training camp and how do they work? - The Mirror US
Cowboys Players Wearing Strange New Helmets at Training Camp – NBC 5 Dallas-Fort Worth
Guardian cap' to prevent head injuries mandated for practices, CFL says
NFL CMO Dr. Allen Sills explains importance of mandated guardian caps during training camp
Guardian Caps: What are they and why are NFL players wearing them? - Sactown Sports
NFL exec suggests Guardian Caps worn to protect players during practices could one day debut in games
NFL training camps: Guardian Cap players are wearing over helmets, why
Seeking to reduce head contact, NFL mandates use of Guardian Cap helmet for early portion of training camp - ESPN
NFL introduces Guardian Caps across league to limit number of brain injuries in preseason