Guardian Caps - Are the soft-shelled football helmet covers effective at limiting head injuries? - ESPN
Guardian Cap used by football teams to protect against head injury – The Denver Post
NFL's top doctor does not expect Guardian Caps to be worn in games - NBC Sports
Guardian Caps Debut During NFL Minicamps
NFL hopes to reduce head injuries with helmet experiment
Why are NFL players wearing padding on helmets at training camp?
NFL reports reduction in concussions among players who wore Guardian Caps in preseason - The Athletic
NFL hopes to reduce head injuries with helmet experiment
FOOTBALL: Guardian Caps gaining ground as concussion-prevention aid
NFL executive hints that Guardian Caps could eventually be worn in games, along with position-specific helmets
Guardian cap' to prevent head injuries mandated for practices, CFL says
Football Guardian Cap draws mixed reviews from players, experts for safety effectiveness - The Daily Tar Heel
NFL: Concussions dropped by more than 50% among players who wore Guardian Caps during summer