Puffy, spongy Guardian Caps could help curb NFL head injuries - The Washington Post
New helmet design can deal with sports' twists and turns
Examining a Safer Option for Football Helmets
Helmet sticker may reduce concussions
Riddell's Newest Helmet – The Concussion Blog
Football helmet with liquid padding may prevent concussions
Safety first: Lopers to wear padded caps in practice to prevent concussions
UCLA joins program using helmet sensors that monitor head trauma and build data for concussion problem – Orange County Register
What are Guardian Caps? NFL players sport specialty helmets for 2022 minicamp