This washable fine dust filter protects the motor of your vacuum cleaner from dust particles collected in the dust container. To maintain the advanced performance of your Ultra Flex we recommend that you wash the filter regularly. You can do this by removing from the cleaner and washing under running water when it becomes visibly soiled. Allow to air dry before reinserting into your vacuum cleaner. Changing the filter on a regular basis will provide your cleaner with high airflow and strong suction power. This vacuum clear filter pack includes one Ultra Flex fine dust filter. Filter pack reference: EF 129.