Guardian Caps: Why some NFL players are wearing them in training camps
Large Bubble Helmets Are Guardian Caps, NFL's New Safety Measure
Chiefs open camp without star defensive lineman Chris Jones
EXPLAINER: NFL using helmet caps for player safety, research - The San Diego Union-Tribune
Puffy, spongy Guardian Caps could help curb NFL head injuries - The Washington Post
NFL exec suggests Guardian Caps worn to protect players during practices could one day debut in games
Complaints begin regarding Guardian Caps, despite one important hidden benefit - NBC Sports
Guardian cap' to prevent head injuries mandated for practices, CFL says
NFL hopes to reduce head injuries with helmet experiment
NFL CMO Dr. Allen Sills explains importance of mandated guardian caps during training camp
It's time the NFL made Guardian Caps mandatory