Guardian Caps - Are the soft-shelled football helmet covers effective at limiting head injuries? - ESPN
Giants react to NFL's new 'Guardian Caps' at training camps - Big Blue View
What are the padded helmets players are wearing at NFL training camps?
Guardian Cap Debuts at Training Camps League-wide
NFL executive hints that Guardian Caps could eventually be worn in games, along with position-specific helmets
Guardian Caps debut at training camps throughout NFL
GUARDIAN CAP DEBUTS AT TRAINING CAMPS LEAGUE-WIDE
Guardian Caps: Why some NFL players are wearing them in training camps
NFL hopes to reduce head injuries with helmet experiment