NFL training camps: Guardian Cap players are wearing over helmets, why
Varsity Football Helmet Ratings
Guardian Caps: NFL requires use of helmet cover at training camps to reduce head injuries
Puffy, spongy Guardian Caps could help curb NFL head injuries - The Washington Post
Complaints begin regarding Guardian Caps, despite one important hidden benefit - NBC Sports
Guardian Cap - Soft-Shell Protective Helmet Cover : Football Helmets : Sports & Outdoors
The story behind those soft-shell puffy Guardian Caps players have been wearing
Guardian Cap - Soft-Shell Protective Helmet Cover : Football Helmets : Sports & Outdoors
New Football Helmet Could Save the Sport