Why the Ticats are wearing those giant helmets at practice
NFL hopes to reduce head injuries with helmet experiment – The Morning Call
Puffy, spongy Guardian Caps could help curb NFL head injuries - The Washington Post
Guardian Cap used by football teams to protect against head injury – The Denver Post
Soft Protective Headgear Buy Soft Shell Helmets & Protective Padded Equipment Online - GameBreaker
The story behind those soft-shell puffy Guardian Caps players have been wearing
For Giants and the NFL, it's the Summer of Guardian Caps - Newsday
Here's why some Patriots players are wearing caps over their helmets during training camp
Guardian Caps - Are the soft-shelled football helmet covers effective at limiting head injuries? - ESPN