Guardian Cap: What are and why the NFL asks this safety measure in helmets
Guardian Caps - Are the soft-shelled football helmet covers effective at limiting head injuries? - ESPN
Packers share thoughts on wearing Guardian Caps at camp
What are NFL players wearing on their helmets at training camp and how do they work? - The Mirror US
NFL players experiment with 'Guardian Caps' to protect heads
Guardian Caps - Are the soft-shelled football helmet covers effective at limiting head injuries? - ESPN
Padded helmet cover shows little protection for football players - Scope
Guardian Caps leave some NFL players and coaches with concerns: 'You feel like a bobblehead'
Coverage of the NFL in Guardian Caps
NFL executive hints that Guardian Caps could eventually be worn in games, along with position-specific helmets
Seeking to reduce head contact, NFL mandates use of Guardian Cap helmet for early portion of training camp - ESPN
NFL exec suggests Guardian Caps worn to protect players during practices could one day debut in games
Guardian Caps: What are they and why are NFL players wearing them? - Sactown Sports