Asked and Answered: June 14
Guardian Caps: What Are They & How Do They Work?
Concussions: Can cap keep football players' heads in game? – Orange County Register
New Football Helmet Could Save the Sport
What are Guardian Caps? NFL's latest padded helmets for added safety
Florio PFT] The Guardian Cap apparently works. But if a player asks to wear it in a game, the league would say no. : r/nfl
Guardian Caps a fit for Park Wolfpack - Cottage Grove Journal
Guardian cap' to prevent head injuries mandated for practices, CFL says
EXPLAINER: NFL using helmet caps for player safety, research