As NFL mandates Guardian caps in practice, area high school football teams have been using them for years, Sports
The story behind those soft-shell puffy Guardian Caps players have been wearing
More Guardian Caps, And '0' On The Field
Have you seen the strange helmets Cowboys players are wearing in camp? Here's the story
Raiders, other NFL teams wear Guardian Caps for head safety, Raiders News
Guardian Caps - Are the soft-shelled football helmet covers effective at limiting head injuries? - ESPN
NFL players beginning to adopt protective Guardian Caps over helmets at practice - NBC Sports
Coverage of the NFL in Guardian Caps
Guardian Caps: What are they and why are NFL players wearing them? - Sactown Sports
Guardian Caps: Why some NFL players are wearing them in training camps