As NFL mandates Guardian caps in practice, area high school football teams have been using them for years, Sports
Guardian Caps - Are the soft-shelled football helmet covers effective at limiting head injuries? - ESPN
Park High School football blazes safety trail with Guardian Caps
Guardian Caps: What Are They & How Do They Work?
Guardian Caps - Are the soft-shelled football helmet covers effective at limiting head injuries? - ESPN
Concussions: Can cap keep football players' heads in game? – Orange County Register
Guardian cap' to prevent head injuries mandated for practices, CFL says
NFL Presents: League-wide Guardian Cap Use to Reduce Head Impacts
More Guardian Caps, And '0' On The Field
CFL players adjust to their bigger heads, helmet covers worn in practice