Bontrager Rally WaveCel Mountain Bike Helmet: An off-road helmet with WaveCel technology that balances comfort and performance for trail riders who value safety. A major advancement in the protection against cycling-related head injuries Rally WaveCel is a high-style, high-value off-road helmet with trail-specific features and WaveCel, a leading technology in the protection against cycling-related head injuries. WaveCel is a collapsible cellular structure that lines the inside of the helmet. This Bontrager-exclusive technology disrupts the safety standards that the industry has accepted for over 30 years.