Pre-filter, also called a rain sock. Designed for riding in adverse weather conditions, extreme rain, dust etc. without restricting airflow. - 100% monofilament polyester with water repellent finish - Hydrophobic technology repels water in most all riding conditions - Installs over the oval air cleaner in seconds. Note: Compatible with Arlen Ness Stage II Oval Upgrade air cleaner kits only, which are compatible with the OEM oval H-D / Screamin' Eagle Ventilator backing plate for M8 models only. Note: Not compatible with Arlen Ness Method or Stage II Method oval air cleaner assemblies.