NFL players don Guardian Caps, designed to protect from concussion
NFL Presents: League-wide Guardian Cap Use to Reduce Head Impacts
Steelers debut new, safer helmets for off-season training
Steelers debut new, safer helmets for off-season training
What are Guardian Caps and how are they helping football teams?
More padding the issue of concussions and better helmets
NFL training camps: Guardian Cap players are wearing over helmets, why
Get A Load Of These Big Dumb Helmet Helmets
NFL hopes to reduce head injuries with helmet experiment
Puffy, spongy Guardian Caps could help curb NFL head injuries - The Washington Post