Football helmet with liquid padding may prevent concussions
Guardian Caps Guardian Sports
Guardian Cap used by football teams to protect against head injury – The Denver Post
Guardian Cap The Growth of a Game
Creekside High football player dies after being injured
What are Guardian Caps? NFL's latest padded helmets for added safety
Staples football pioneers use of 'Guardian Caps'
What are Guardian Caps? Shadow Hills football using new device to reduce head injuries
Concussions: Can cap keep football players' heads in game? – Orange County Register