Chicago Bears: Why players are wearing padded helmets
Guardian Cap Debuts at Training Camps League-wide
Guardian Caps - Are the soft-shelled football helmet covers effective at limiting head injuries? - ESPN
Puffy, spongy Guardian Caps could help curb NFL head injuries - The Washington Post
Guardian Caps: Why some NFL players are wearing them in training camps
Guardian Cap debuts during minicamps in effort to reduce avoidable head contact
What are those caps football players are wearing?
NFL training camps: Guardian Cap players are wearing over helmets, why