Guardian Caps Guardian Sports
Find out how modern football helmets attempt to limit brain injuries
Not Safe for Children? Football's Leaders Make Drastic Changes to Youth Game - The New York Times
EXPLAINER: NFL using helmet caps for player safety, research - The San Diego Union-Tribune
Football Helmets, Shoulder Pads, Facemasks, Xenith
Style vs safety: Do too many football helmets pose a risk?
Seattle Seahawks safety Jamal Adams leaves first game in more than a year with a concussion
Helmets don't eliminate concussions. It's time for the NFL to ditch them, NFL
Guardian Caps - Are the soft-shelled football helmet covers effective at limiting head injuries? - ESPN