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. Twin Air filters are designed to increase airflow while ensuring the highest level of protection from dirt / dust. Washable / reusable - reusing a Twin Air filter 40 - 50 times is common. High quality - assembled by hand and inspected for a perfect fit. Coarse open-pore foam catches airborne dirt, grime and sand.