Playing with a pillow on your head': Buffalo Bills embrace new helmet covers
Guardian Caps debut at training camps throughout NFL
Guardian Cap: What are and why the NFL asks this safety measure in helmets
Large Bubble Helmets Are Guardian Caps, NFL's New Safety Measure
Xaverian High in Mass. introduces Guardian Caps for football players
Guardian Cap used by football teams to protect against head injury – The Denver Post
What are NFL players wearing on their helmets at training camp and how do they work? - The Mirror US
As NFL mandates Guardian caps in practice, area high school football teams have been using them for years, Sports
NFL Mandated Guardian Caps: Controversial Change - Sports Illustrated Seattle Seahawks News, Analysis and More
Puffy, spongy Guardian Caps could help curb NFL head injuries - The Washington Post
Giants react to NFL's new 'Guardian Caps' at training camps - Big Blue View
NFL Players Experiment With 'Guardian Caps' to Protect Heads – NBC Connecticut
NFL hopes to reduce head injuries with helmet experiment
NFL players wear Guardian Caps to reduce head trauma during training camp
EXPLAINER: NFL using helmet caps for player safety, research - The San Diego Union-Tribune