Replacement iRobot Roomba 4000 Side Brush and Filters Replacement - Kit Includes 1 Side Brushes and 1 Filters iRobot Roomba 4000 Side Brush and Filters Replacement Kit Includes 1 Side Brushes and 1 Filters It's best to replace your filters and brushes every 1 to 2 months The Brush allows your Roomba to reach deeper into the carpet for a more thorough cleaning Filters reduce infiltration of dust, pollen and other allergens