Guardian Caps NFL: What player positions are required to wear them?
The story behind those soft-shell puffy Guardian Caps players have been wearing
What are those caps football players are wearing?
Patriots, rest of NFL wearing cushioned helmet caps at training camp, per new mandate - CBS Boston
Patriots Training Camp Recap: Trent Brown returns for full pads work - Pats Pulpit
Patriots and Packers get into numerous scraps, and other takeways from Day 2 of joint practice - The Boston Globe
Guardian Caps - Are the soft-shelled football helmet covers effective at limiting head injuries? - ESPN
NFL Training Camp: 12 photos of players wearing the new Guardian Caps
Here's why some Patriots players are wearing caps over their helmets during training camp
Why are players wearing padded helmets at NFL training camps?