The phrase "special helmet" refers to a unique or customized protective headgear worn by someone for a particular purpose or situation to keep their head safe. Full definition
Mississippi State will wear special helmet decals in honor of the victims of Hurricane Harvey in Texas. (wtvm.com)
Pascal Wehrlein's 2017 Singapore GP special helmet. (wtf1.com)
Unity High School in Tolono, Ill., has equipped its 32 varsity football team members with special helmets that employ Head Impact Telemetry System (HITS) technology. (scientificamerican.com)