WRSI Trident Helmet WRSI stands for Whitewater Research and Safety Institute, an organization founded to advance whitewater safety awareness and technology. A rugged carbon-composite shell combines with an EVA foam liners and a polyurethane sub-shell to effectively dissipate impacts. Soft EVA foam pads line the sub-shell for extra protection and comfort. They attach with hook-and-loop patches. The Interconnect Retention System works as an adjustable harness to ensure a safe and secure fit. Sizing for Small/Med: Head Circumference 19 to 21-1/2 inches (48-55 cm); fitted hat size 6 to 6- 7/8