This is where it all began. Over 40 years ago, the sandy, gritty soil of The Netherlands – and the resulting engine failures – proved that single-foam and paper filters gave riders air flow, but failed at protection. Twin Air’s breakthrough, fused-dual-layer design (now widely copied) combined performance and protection. The fused layers of open-pore foam and fine inner foam trap even the smallest particles. The new, rounder design boosts airflow. So do the minimized seams made possible by a revolutionary micro-gluing process: Shorter seams = more foam = more flow.