HKS replacement Filter Elements are available in a dry 3 layer, triple density or wet 2 layer, dual density construction. The dry 3 layer type is standard in SMF Reloaded Intake kits, and is designed for superior filtration while still providing excellent airflow. The wet 2 layer type is included in Racing Suction kits and is focused on maximizing airflow for performance, yet still keeping harmful particles from the engine. If your vehicle is in a high dust area, HKS recommends using dry 3 layer elements.