NFL training camps: Guardian Cap players are wearing over helmets, why
Guardian Caps debut at NFL training camps around the league
NFL executive hints that Guardian Caps could eventually be worn in games, along with position-specific helmets
What's with padded helmet caps teams are wearing
Guardian Caps: The new helmets worn by several NFL teams
Why are NFL players wearing padding on helmets at training camp?
Puffy Guardian Caps Could Reduce NFL Player Concussions
NFL executive: Guardian Caps could one day be used in games
NFL players experiment with 'Guardian Caps' to protect heads
Browns wearing Guardian Caps during training camp