NFL's use of Guardian padded helmet caps in camp draws support and skepticism - The Athletic
Guardian Caps Debut at Training Camps Across the NFL
NFL players wear Guardian Caps to reduce head trauma during training camp
What are NFL players wearing on their helmets at training camp and how do they work? - The Mirror US
If a player wanted to wear a Guardian Cap during a game, the league would prohibit it - NBC Sports
Coverage of the NFL in Guardian Caps
Guardian Caps Debut During NFL Minicamps
Padded helmet cover shows little protection for football players - Scope
EXPLAINER: NFL using helmet caps for player safety, research - The San Diego Union-Tribune
NFL Guardian Caps: How Do They Work? – NBC 6 South Florida
Here's why some Patriots players are wearing caps over their helmets during training camp
Guardian Cap Debuts at Training Camps League-wide
Guardian Cap Use a Concern for Watt, Saleh Early in Training Camp - Sports Illustrated
Guardian Cap Debuts at Training Camps League-wide
Guardian Cap debuts during minicamps in effort to reduce avoidable head contact