Guardian Caps: Why some NFL players are wearing them in training camps
Guardian cap' to prevent head injuries mandated for practices, CFL says
NFL executive hints that Guardian Caps could eventually be worn in games, along with position-specific helmets
NFL hopes to reduce head injuries with helmet experiment
What Pros Wear: Guardian Caps What are Those Helmet Covers Being Worn in Practice? - What Pros Wear
NFL Introduces Guardian Caps At First Week Of Training Camp - The Sports Credential
Guardian Caps Guardian Sports
NFL players experiment with Guardian Caps // Guardian Sports
What are Guardian Caps and how are they helping football teams?
Guardian Cap Debuts at Training Camps League-wide
First QB helmet designed to help reduce concussions approved by NFL, NFLPA
What are those funny-looking soft caps on NFL helmets during camp?, Sports