Prior to the 1920s, miners wore a soft cap made of cloth or canvas with a leather brim and lamp bracket to hold their light. But in 1919, Edward D. Bullard of San Francisco, California developed the ...

Among those players is Damar Hamlin, who recently started wearing the Guardian Cap over his helmet in the Bills' preseason games. What exactly are Guardian Caps, and how effective are they?

It wraps around the outer shell of a player’s helmet, and has foam blocks that absorb energy when hit. During games, a swim-cap-like cloth designed to look like a regular helmet goes over the ...