Colleges add Guardian football protective helmet cap - Sports Illustrated
Guardian Protective Helmet Cover - XT Model
The Fruitless Search for a 'Concussion-Proof' Football Helmet - The Atlantic
Guardian Caps: NFL requires use of helmet cover at training camps to reduce head injuries
The Extra Yard: The Ins and Outs of an American Football Helmet - Stories
Large Bubble Helmets Are Guardian Caps, NFL's New Safety Measure
Can Custom-Fit Football Helmets Protect Athletes From Brain Trauma?, Chicago News
NFL's use of Guardian padded helmet caps in camp draws support and skepticism - The Athletic
Football helmets with outside padding get tryout at high schools