NFL's use of Guardian padded helmet caps in camp draws support and skepticism - The Athletic
NFL hopes to reduce head injuries with helmet experiment
Guardian Caps, a soft-shell helmet cover, among CFL's new player-safety initiatives
Guardian cap' to prevent head injuries mandated for practices, CFL says
NFL Health and Safety Fact Sheet
NFL players don Guardian Caps, designed to protect from concussion
What Pros Wear: Guardian Caps What are Those Helmet Covers Being Worn in Practice? - What Pros Wear
Cowboys seen wearing protective, NFL mandated Guardian Caps at OTAs
A shocking resolution regarding Guardian Caps is being considered by the League. - The Wood Cafe