Guardian Caps: Why some NFL players are wearing them in training camps
Guardian Caps - Are the soft-shelled football helmet covers effective at limiting head injuries? - ESPN
Why the Ticats are wearing those giant helmets at practice
EXPLAINER: NFL using helmet caps for player safety, research
NFL training camps: Guardian Cap players are wearing over helmets, why
NFL hopes to reduce head injuries with 'goofy' helmet experiment
Guardian cap' to prevent head injuries mandated for practices, CFL says
NFL players experimenting with 'Guardian Caps' to prevent head injuries
NFL allowing players to wear lightly tinted Oakley helmet visors - Sports Illustrated
Guardian Cap debuts during minicamps in effort to reduce avoidable head contact
NFL hopes to reduce head injuries with helmet experiment
Puffy, spongy Guardian Caps could help curb NFL head injuries - The Washington Post
Video: CFL players adjust to protective helmet caps - The Globe and Mail
Rules for Football Helmets and Face Masks - dummies
Edmonton error: press release gaffe exposes potential CFL salary cap collusion - 3DownNation