NFL players experiment with 'Guardian Caps' to protect heads
NFL's use of Guardian padded helmet caps in camp draws support and skepticism - The Athletic
NFL players wear Guardian Caps to reduce head trauma during training camp
Truth About Guardian Caps
NFL CMO Dr. Allen Sills explains importance of mandated guardian caps during training camp
What are NFL players wearing on their helmets at training camp and how do they work? - The Mirror US
Large Bubble Helmets Are Guardian Caps, NFL's New Safety Measure
NFL exec suggests Guardian Caps worn to protect players during practices could one day debut in games
EXPLAINER: NFL using helmet caps for player safety, research - The San Diego Union-Tribune
Guardian Cap debuts during minicamps in effort to reduce avoidable head contact