Padded helmet cover shows little protection for football players - Scope
CWU football players wear extra helmet layer to prevent concussions
Puffy, spongy Guardian Caps could help curb NFL head injuries - The Washington Post
Guardian Caps: What are they and why are NFL players wearing them? - Sactown Sports
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
Guardian Caps: NFL requires use of helmet cover at training camps to reduce head injuries
Why are NFL players wearing padding on helmets at training camp?
NFL training camps: Guardian Cap players are wearing over helmets, why
New NFL Helmets - NFL Testing Validates Benefit of Guardian Caps
Large Bubble Helmets Are Guardian Caps, NFL's New Safety Measure
NFL players don Guardian Caps, designed to protect from concussion
What Pros Wear: Guardian Caps What are Those Helmet Covers Being Worn in Practice? - What Pros Wear
NFL concussions Guardian Cap - TSN.ca
NFL Executive VP: League Saw 52 Percent Decrease In Concussions At Positions Wearing Guardian Caps - Steelers Depot