Such grim examples have spawned the first major efforts to redesign the football helmet since the 1950s, along with new rules for playing the game. The largest U.S. helmet manufacturers, as well as independent designers, are testing novel ways to cushion big and small blows to the head, or to provide immediate relief in the minutes after a major injury. ... Model High last year became one of the first high schools to experiment with a helmet cover developed by The Hanson Group of Alpharetta, Georgia and Protective Sports Equipment of Edinboro, Pennsylvania. The cover, dubbed the Guardian, has 37 gel-filled pouches that fit over a helmet and cushion against helmet-to-helmet blows that are so dangerous that the NFL aggressively penalizes them. ... Based on an idea developed by Brazilian neuroscientist Renato Rozental, the device is a bladder that can fit inside a player’s helmet. In the event of a hard hit to the head, a trainer or teammate would attach a source of cooling gas to the bladder to lower the head’s temperature and stave off damage. The effect would be similar to applying an ice pack.