Here's why some Patriots players are wearing caps over their helmets during training camp
Guardian Cap: What are and why the NFL asks this safety measure in helmets
NFL executive: Guardian Caps could one day be used in games
What are Guardian Caps and how are they helping football teams?
Padded helmet cover shows little protection for football players - Scope
Guardian Caps (@guardian_caps) • Instagram photos and videos
NFL hopes to reduce head injuries with helmet experiment - The San Diego Union-Tribune
EXPLAINER: NFL using helmet caps for player safety, research
Concussions among players who wore Guardian Caps over summer dropped more than 50%, NFL says - ESPN
Guardian Football Caps XT, Light Silver White / OFSA
Guardian' helmet caps help protect Herd linemen, Marshall Sports