Large Bubble Helmets Are Guardian Caps, NFL's New Safety Measure
Here's why some Patriots players are wearing caps over their helmets during training camp
NFL's use of Guardian padded helmet caps in camp draws support and skepticism - The Athletic
NFL's top doctor does not expect Guardian Caps to be worn in games - NBC Sports
Guardian Caps: NFL requires use of helmet cover at training camps to reduce head injuries
Padded helmet cover shows little protection for football players - Scope
How the NFL plans to play a season during the pandemic
NFL: Concussions dropped by more than 50% among players who wore Guardian Caps during summer
Guardian Caps - Are the soft-shelled football helmet covers effective at limiting head injuries? - ESPN