Why do some helmets on NFL players have a hexagonal cutout on them (and some do not)? - Quora
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The Safest Football Helmet Is Not Yet a Hit in the NFL - WSJ
Vicis football helmet unboxing: Watch a high school linebacker open his new high-tech head protector – GeekWire
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New D-III helmets take a page from the Pro Combat lids - Footballscoop
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